diff --git a/CHANGELOG-WIP.md b/CHANGELOG-WIP.md
index aa5c1d6e11..f9888df676 100644
--- a/CHANGELOG-WIP.md
+++ b/CHANGELOG-WIP.md
@@ -1,5 +1,9 @@
 # Release Notes for Craft Commerce (WIP)
 
+### Fixed
+
+- Fixed a PHP error that could occur when calculating tax totals. ([#3822](https://github.com/craftcms/commerce/issues/3822))
+
 ### Store Management
 - It is now possible to design card views for Products and Variants. ([#3809](https://github.com/craftcms/commerce/pull/3809))
 - Order conditions can now have a “Coupon Code” rule. ([#3776](https://github.com/craftcms/commerce/discussions/3776))
@@ -16,15 +20,21 @@
 - Added an `originalCart` value to `commerce/update-cart` action, for failed ajax responses. ([#430](https://github.com/craftcms/commerce/issues/430))
 
 ### Extensibility
+- Added `craft\commerce\base\Purchasable::hasInventory()`.
 - Added `craft\commerce\base\InventoryItemTrait`.
 - Added `craft\commerce\base\InventoryLocationTrait`.
+- Added `craft\commerce\elements\Purchasable::$allowOutOfStockPurchases`.
+- Added `craft\commerce\elements\Purchasable::getIsOutOfStockPurchasingAllowed()`.
 - Added `craft\commerce\elements\conditions\orders\CouponCodeConditionRule`.
 - Added `craft\commerce\elements\conditions\variants\ProductConditionRule`.
 - Added `craft\commerce\elements\db\OrderQuery::$couponCode`.
 - Added `craft\commerce\elements\db\OrderQuery::couponCode()`.
 - Added `craft\commerce\events\CartPurgeEvent`.
+- Added `craft\commerce\events\PurchasableOutOfStockPurchasesAllowedEvent`.
 - Added `craft\commerce\services\Inventory::updateInventoryLevel()`.
 - Added `craft\commerce\services\Inventory::updatePurchasableInventoryLevel()`.
+- Added `craft\commerce\services\Purchasables::EVENT_PURCHASABLE_OUT_OF_STOCK_PURCHASES_ALLOWED`.
+- Added `craft\commerce\services\Purchasables::isPurchasableOutOfStockPurchasingAllowed()`.
 
 ### System
 - Craft Commerce now requires Craft CMS 5.5 or later.
diff --git a/example-templates/dist/shop/products/_includes/grid.twig b/example-templates/dist/shop/products/_includes/grid.twig
index 58dab092f7..1e7e3c01e0 100644
--- a/example-templates/dist/shop/products/_includes/grid.twig
+++ b/example-templates/dist/shop/products/_includes/grid.twig
@@ -50,7 +50,16 @@
                     checked: loop.first,
                     class: not variant.getIsAvailable() ? 'opacity-10' : '',
                     disabled: not variant.availableForPurchase,
-                  }) }}<span class="pl-1">{{ variant.sku }} {% if variant.inventoryTracked %}({{ variant.stock ? variant.stock ~ ' available' : 'out of stock'}}){% endif %}</span><span class="ml-auto">{% if variant.onPromotion %} <del class="text-gray-400 text-xs">{{ variant.price|currency(cart.currency) }}</del>{% endif %} {{ variant.salePrice|currency(cart.currency) }}</span>
+                  }) }}
+                  <span class="pl-1">{{ variant.sku }}
+                    {% if variant.hasInventory and variant.inventoryTracked %}
+                      ({{ variant.stock ? variant.stock ~ ' available' : 'out of stock'}})
+                      {% if variant.allowOutOfStockPurchases %}
+                        <span class="text-xs text-gray-400">{{ "Continue selling when out of stock."|t('commerce') }}</span>
+                      {% endif %}
+                    {% endif %}
+                  </span>
+                  <span class="ml-auto">{% if variant.onPromotion %} <del class="text-gray-400 text-xs">{{ variant.price|currency(cart.currency) }}</del>{% endif %} {{ variant.salePrice|currency(cart.currency) }}</span>
                 </label>
               {% endfor %}
             </div>
diff --git a/example-templates/src/shop/products/_includes/grid.twig b/example-templates/src/shop/products/_includes/grid.twig
index de1db79777..8043b860ec 100644
--- a/example-templates/src/shop/products/_includes/grid.twig
+++ b/example-templates/src/shop/products/_includes/grid.twig
@@ -50,7 +50,16 @@
                     checked: loop.first,
                     class: not variant.getIsAvailable() ? 'opacity-10' : '',
                     disabled: not variant.availableForPurchase,
-                  }) }}<span class="pl-1">{{ variant.sku }} {% if variant.inventoryTracked %}({{ variant.stock ? variant.stock ~ ' available' : 'out of stock'}}){% endif %}</span><span class="ml-auto">{% if variant.onPromotion %} <del class="text-gray-400 text-xs">{{ variant.price|currency(cart.currency) }}</del>{% endif %} {{ variant.salePrice|currency(cart.currency) }}</span>
+                  }) }}
+                  <span class="pl-1">{{ variant.sku }}
+                    {% if variant.hasInventory and variant.inventoryTracked %}
+                      ({{ variant.stock ? variant.stock ~ ' available' : 'out of stock'}})
+                      {% if variant.allowOutOfStockPurchases %}
+                        <span class="text-xs text-gray-400">{{ "Continue selling when out of stock."|t('commerce') }}</span>
+                      {% endif %}
+                    {% endif %}
+                  </span>
+                  <span class="ml-auto">{% if variant.onPromotion %} <del class="text-gray-400 text-xs">{{ variant.price|currency(cart.currency) }}</del>{% endif %} {{ variant.salePrice|currency(cart.currency) }}</span>
                 </label>
               {% endfor %}
             </div>
diff --git a/src/Plugin.php b/src/Plugin.php
index c809208c7d..7c0182da97 100755
--- a/src/Plugin.php
+++ b/src/Plugin.php
@@ -257,7 +257,7 @@ public static function editions(): array
     /**
      * @inheritDoc
      */
-    public string $schemaVersion = '5.2.9.1';
+    public string $schemaVersion = '5.3.0.2';
 
     /**
      * @inheritdoc
diff --git a/src/adjusters/Tax.php b/src/adjusters/Tax.php
index 28211077d0..d854c34187 100644
--- a/src/adjusters/Tax.php
+++ b/src/adjusters/Tax.php
@@ -22,6 +22,7 @@
 use DvK\Vat\Validator;
 use Exception;
 use Illuminate\Support\Collection;
+use Money\Teller;
 use yii\base\InvalidConfigException;
 use function in_array;
 
@@ -78,12 +79,47 @@ class Tax extends Component implements AdjusterInterface
     private float $_costRemovedForOrderShipping = 0;
 
     /**
-     * Track the additional discounts created inside the tax adjuster for order total price
+     * Track the additional discounts created inside the tax adjuster for order shipping
+     * This should not be modified directly, use _addAmountRemovedForOrderShipping() instead
      *
      * @var float
+     * @see _addAmountRemovedForOrderTotalPrice()
      */
     private float $_costRemovedForOrderTotalPrice = 0;
 
+    /**
+     * The way to internally interact with the _costRemovedForOrderShipping property
+     *
+     * @param float $amount
+     * @return void
+     * @throws Exception
+     */
+    private function _addAmountRemovedForOrderShipping(float $amount): void
+    {
+        if ($amount < 0) {
+            throw new Exception('Amount added to the total removed shipping must be a positive number');
+        }
+
+        $this->_costRemovedForOrderShipping += $amount;
+    }
+
+
+    /**
+     * The way to interact with the _costRemovedForOrderTotalPrice property
+     *
+     * @param float $amount
+     * @return void
+     * @throws Exception
+     */
+    private function _addAmountRemovedForOrderTotalPrice(float $amount): void
+    {
+        if ($amount < 0) {
+            throw new Exception('Amount added to the total removed price must be a positive number');
+        }
+
+        $this->_costRemovedForOrderTotalPrice = $this->_getTeller()->add($this->_costRemovedForOrderTotalPrice, $amount);
+    }
+
     /**
      * @inheritdoc
      */
@@ -125,6 +161,7 @@ private function _getAdjustments(TaxRate $taxRate): array
     {
         $adjustments = [];
         $hasValidEuVatId = false;
+        $teller = $this->_getTeller();
 
         $zoneMatches = $taxRate->getIsEverywhere() || ($taxRate->getTaxZone() && $this->_matchAddress($taxRate->getTaxZone()));
 
@@ -136,7 +173,7 @@ private function _getAdjustments(TaxRate $taxRate): array
         $removeDueToVat = ($zoneMatches && $hasValidEuVatId && $taxRate->removeVatIncluded);
         if ($removeIncluded || $removeDueToVat) {
 
-            // Is this an order level tax rate?
+            // Remove included tax for order level taxable.
             if (in_array($taxRate->taxable, TaxRateRecord::ORDER_TAXABALES, false)) {
                 $orderTaxableAmount = 0;
 
@@ -146,41 +183,68 @@ private function _getAdjustments(TaxRate $taxRate): array
                     $orderTaxableAmount = $this->_order->getTotalShippingCost();
                 }
 
-                $amount = -$this->_getTaxAmount($orderTaxableAmount, $taxRate->rate, $taxRate->include);
+                $orderLevelAmountToBeRemovedByDiscount = $this->_getTaxAmount($orderTaxableAmount, $taxRate->rate, $taxRate->include);
 
                 if ($taxRate->taxable === TaxRateRecord::TAXABLE_ORDER_TOTAL_PRICE) {
-                    $this->_costRemovedForOrderTotalPrice += $amount;
+                    $this->_addAmountRemovedForOrderTotalPrice($orderLevelAmountToBeRemovedByDiscount);
                 } elseif ($taxRate->taxable === TaxRateRecord::TAXABLE_ORDER_TOTAL_SHIPPING) {
-                    $this->_costRemovedForOrderShipping += $amount;
+                    $this->_addAmountRemovedForOrderShipping($orderLevelAmountToBeRemovedByDiscount);
                 }
 
                 $adjustment = $this->_createAdjustment($taxRate);
                 // We need to display the adjustment that removed the included tax
                 $adjustment->name = Craft::t('site', $taxRate->name) . ' ' . Craft::t('commerce', 'Removed');
-                $adjustment->amount = $amount;
+                $adjustment->amount = -$orderLevelAmountToBeRemovedByDiscount;
                 $adjustment->type = 'discount'; // TODO Not use a discount adjustment, but modify the price of the item instead. #COM-26
                 $adjustment->included = false;
 
                 $adjustments[] = $adjustment;
             }
 
+            // Not an order level taxable, add tax adjustments to the line items.
             if (!in_array($taxRate->taxable, TaxRateRecord::ORDER_TAXABALES, false)) {
                 // Not an order level taxable, add tax adjustments to the line items.
                 foreach ($this->_order->getLineItems() as $item) {
                     if ($item->taxCategoryId == $taxRate->taxCategoryId) {
                         if ($taxRate->taxable == TaxRateRecord::TAXABLE_PURCHASABLE) {
-                            $taxableAmount = $item->salePrice - Currency::round($item->getDiscount() / $item->qty);
-                            $amount = -($taxableAmount - ($taxableAmount / (1 + $taxRate->rate)));
-                            $amount = $amount * $item->qty;
+                            // taxableAmount = salePrice - (discount / qty)
+                            $taxableAmount = $teller->subtract(
+                                $item->salePrice,
+                                $teller->divide(
+                                    $item->getDiscount(), // float amount of discount
+                                    $item->qty
+                                )
+                            );
+
+                            // amount = taxableAmount - (taxableAmount / (1 + taxRate))
+                            $amount = $teller->subtract(
+                                $taxableAmount,
+                                $teller->divide(
+                                    $taxableAmount,
+                                    (1 + $taxRate->rate)
+                                )
+                            );
+
+                            // make amount negative
+                            $amount = (float)$teller->multiply($amount, $item->qty);
                         } else {
                             $taxableAmount = $item->getTaxableSubtotal($taxRate->taxable);
-                            $amount = -($taxableAmount - ($taxableAmount / (1 + $taxRate->rate)));
+                            // amount = taxableAmount - (taxableAmount / (1 + taxRate))
+                            $amount = $teller->subtract(
+                                $taxableAmount,
+                                $teller->divide(
+                                    $taxableAmount,
+                                    (1 + $taxRate->rate)
+                                )
+                            );
+
+                            // make amount negative
+                            $amount = (float)$amount;
                         }
-                        $amount = Currency::round($amount);
                         $adjustment = $this->_createAdjustment($taxRate);
                         // We need to display the adjustment that removed the included tax
                         $adjustment->name = Craft::t('site', $taxRate->name) . ' ' . Craft::t('commerce', 'Removed');
-                        $adjustment->amount = $amount;
+                        $adjustment->amount = -$amount;
                         $adjustment->setLineItem($item);
                         $adjustment->type = 'discount';
                         $adjustment->included = false;
@@ -197,6 +261,7 @@ private function _getAdjustments(TaxRate $taxRate): array
                     }
                 }
             }
+
             // Return the removed included taxes as discounts.
             return $adjustments;
         }
@@ -301,17 +366,16 @@ protected function getTaxRates(?int $storeId = null): Collection
      */
     private function _getTaxAmount($taxableAmount, $rate, $included): float
     {
+        $teller = $this->_getTeller();
         if (!$included) {
-            $incTax = $taxableAmount * (1 + $rate);
-            $incTax = Currency::round($incTax);
-            $tax = $incTax - $taxableAmount;
+            $incTax = $teller->multiply($taxableAmount,  (1 + $rate));
+            $tax = $teller->subtract($incTax, $taxableAmount);
         } else {
-            $exTax = $taxableAmount / (1 + $rate);
-            $exTax = Currency::round($exTax);
-            $tax = $taxableAmount - $exTax;
+            $exTax = $teller->divide($taxableAmount, (1 + $rate));
+            $tax = $teller->subtract($taxableAmount, $exTax);
         }
 
-        return $tax;
+        return (float)$tax;
     }
 
     /**
@@ -433,4 +497,14 @@ private function _getTaxAddress(): ?Address
 
         return $address;
     }
+
+    /**
+     * @return Teller
+     * @throws InvalidConfigException
+     * @since 5.3.0
+     */
+    private function _getTeller(): Teller
+    {
+        return Plugin::getInstance()->getCurrencies()->getTeller($this->_order->currency);
+    }
 }
diff --git a/src/base/Purchasable.php b/src/base/Purchasable.php
index 7ac8cf2de2..e80c55ca24 100644
--- a/src/base/Purchasable.php
+++ b/src/base/Purchasable.php
@@ -12,6 +12,7 @@
 use craft\base\NestedElementInterface;
 use craft\commerce\db\Table;
 use craft\commerce\elements\Order;
+use craft\commerce\enums\LineItemType;
 use craft\commerce\errors\StoreNotFoundException;
 use craft\commerce\helpers\Currency;
 use craft\commerce\helpers\Localization;
@@ -228,6 +229,14 @@ abstract class Purchasable extends Element implements PurchasableInterface, HasS
      */
     public bool $inventoryTracked = false;
 
+    /**
+     * Should this purchases of this purchasable be allowed if it is out of stock.
+     *
+     * @var bool
+     * @since 5.3.0
+     */
+    public bool $allowOutOfStockPurchases = false;
+
     /**
      * This is the cached total available stock across all inventory locations.
      *
@@ -254,6 +263,8 @@ public function attributes(): array
         $names[] = 'sku';
         $names[] = 'stock';
         $names[] = 'inventoryTracked';
+        $names[] = 'allowOutOfStockPurchases';
+
         return $names;
     }
 
@@ -443,16 +454,17 @@ public function getIsAvailable(): bool
             return false;
         }
 
-        // Is the inventory tracked and is there stock?
-        if ($this->inventoryTracked && $this->getStock() < 1) {
-            return false;
-        }
-
         // Temporary SKU can not be added to the cart
         if (PurchasableHelper::isTempSku($this->getSku())) {
             return false;
         }
 
+        if (static::hasInventory() && $this->inventoryTracked && $this->getStock() < 1) {
+            if (!Plugin::getInstance()->getPurchasables()->isPurchasableOutOfStockPurchasingAllowed($this)) {
+                return false;
+            }
+        }
+
         return true;
     }
 
@@ -746,7 +758,11 @@ public function populateLineItem(LineItem $lineItem): void
         // Since we do not have a proper stock reservation system, we need deduct stock if they have more in the cart than is available, and to do this quietly.
         // If this occurs in the payment request, the user will be notified the order has changed.
         if (($order = $lineItem->getOrder()) && !$order->isCompleted) {
-            if ($this->inventoryTracked && ($lineItem->qty > $this->getStock())) {
+            if ($this::hasInventory() &&
+                !$this->getIsOutOfStockPurchasingAllowed() &&
+                $this->inventoryTracked &&
+                ($lineItem->qty > $this->getStock())
+            ) {
                 $message = Craft::t('commerce', '{description} only has {stock} in stock.', ['description' => $lineItem->getDescription(), 'stock' => $this->getStock()]);
                 /** @var OrderNotice $notice */
                 $notice = Craft::createObject([
@@ -801,7 +817,7 @@ function($attribute, $params, Validator $validator) use ($lineItem) {
                         $validator->addError($lineItem, $attribute, Craft::t('commerce', 'No purchasable available.'));
                     }
 
-                    if (!$purchasable->getIsAvailable()) {
+                    if (!Plugin::getInstance()->getPurchasables()->isPurchasableAvailable($lineItem->getPurchasable(), $lineItem->getOrder())) {
                         $validator->addError($lineItem, $attribute, Craft::t('commerce', 'The item is not enabled for sale.'));
                     }
                 },
@@ -809,16 +825,24 @@ function($attribute, $params, Validator $validator) use ($lineItem) {
             [
                 'qty',
                 function($attribute, $params, Validator $validator) use ($lineItem, $lineItemQuantitiesById, $lineItemQuantitiesByPurchasableId) {
+                    if ($lineItem->type == LineItemType::Custom) {
+                        return;
+                    }
+
                     if (!$this->hasStock()) {
-                        $error = Craft::t('commerce', '“{description}” is currently out of stock.', ['description' => $lineItem->purchasable->getDescription()]);
-                        $validator->addError($lineItem, $attribute, $error);
+                        if (!Plugin::getInstance()->getPurchasables()->isPurchasableOutOfStockPurchasingAllowed($lineItem->getPurchasable(), $lineItem->getOrder())) {
+                            $error = Craft::t('commerce', '“{description}” is currently out of stock.', ['description' => $lineItem->purchasable->getDescription()]);
+                            $validator->addError($lineItem, $attribute, $error);
+                        }
                     }
 
                     $lineItemQty = $lineItem->id !== null ? $lineItemQuantitiesById[$lineItem->id] : $lineItemQuantitiesByPurchasableId[$lineItem->purchasableId];
 
                     if ($this->hasStock() && $this->inventoryTracked && $lineItemQty > $this->getStock()) {
-                        $error = Craft::t('commerce', 'There are only {num} “{description}” items left in stock.', ['num' => $this->getStock(), 'description' => $lineItem->purchasable->getDescription()]);
-                        $validator->addError($lineItem, $attribute, $error);
+                        if (!Plugin::getInstance()->getPurchasables()->isPurchasableOutOfStockPurchasingAllowed($lineItem->getPurchasable(), $lineItem->getOrder())) {
+                            $error = Craft::t('commerce', 'There are only {num} “{description}” items left in stock.', ['num' => $this->getStock(), 'description' => $lineItem->purchasable->getDescription()]);
+                            $validator->addError($lineItem, $attribute, $error);
+                        }
                     }
 
                     if ($this->minQty > 1 && $lineItemQty < $this->minQty) {
@@ -859,7 +883,7 @@ protected function defineRules(): array
             ],
             [['basePrice'], 'number'],
             [['basePromotionalPrice', 'minQty', 'maxQty'], 'number', 'skipOnEmpty' => true],
-            [['freeShipping', 'inventoryTracked', 'promotable', 'availableForPurchase'], 'boolean'],
+            [['freeShipping', 'inventoryTracked', 'allowOutOfStockPurchases', 'promotable', 'availableForPurchase'], 'boolean'],
             [['taxCategoryId', 'shippingCategoryId', 'price', 'promotionalPrice', 'productSlug', 'productTypeHandle'], 'safe'],
         ]);
     }
@@ -922,7 +946,7 @@ public function getInventoryItem(): InventoryItem
      */
     public function getHasUnlimitedStock(): bool
     {
-        return !$this->inventoryTracked;
+        return !$this::hasInventory() || !$this->inventoryTracked;
     }
 
     /**
@@ -948,6 +972,15 @@ private function _getStock(): int
         return $saleableAmount;
     }
 
+    /**
+     * @return bool
+     * @since 5.3.0
+     */
+    public function getIsOutOfStockPurchasingAllowed(): bool
+    {
+        return Plugin::getInstance()->getPurchasables()->isPurchasableOutOfStockPurchasingAllowed($this);
+    }
+
     /**
      * Returns the cached total available stock across all inventory locations for this store.
      *
@@ -1035,27 +1068,29 @@ public function afterSave(bool $isNew): void
 
             // Always create the inventory item even if it's a temporary draft (in the slide) since we want to allow stock to be
             // added to inventory before it is saved as a permanent variant.
-            if ($canonicalPurchasableId) {
-                if ($isOwnerDraftApplying && $this->duplicateOf !== null) {
-                    /** @var InventoryItemRecord|null $inventoryItem */
-                    $inventoryItem = InventoryItemRecord::find()->where(['purchasableId' => $this->duplicateOf->id])->one();
-                    if ($inventoryItem) {
-                        $inventoryItem->purchasableId = $canonicalPurchasableId;
-                        $inventoryItem->save();
-                        $this->inventoryItemId = $inventoryItem->id;
-                    }
-                } else {
-                    // Set the inventory item data
-                    /** @var InventoryItemRecord|null $inventoryItem */
-                    $inventoryItem = InventoryItemRecord::find()->where(['purchasableId' => $canonicalPurchasableId])->one();
-                    if (!$inventoryItem) {
-                        $inventoryItem = new InventoryItemRecord();
-                        $inventoryItem->purchasableId = $canonicalPurchasableId;
-                        $inventoryItem->countryCodeOfOrigin = '';
-                        $inventoryItem->administrativeAreaCodeOfOrigin = '';
-                        $inventoryItem->harmonizedSystemCode = '';
-                        $inventoryItem->save();
-                        $this->inventoryItemId = $inventoryItem->id;
+            if (static::hasInventory()) {
+                if ($canonicalPurchasableId) {
+                    if ($isOwnerDraftApplying && $this->duplicateOf !== null) {
+                        /** @var InventoryItemRecord|null $inventoryItem */
+                        $inventoryItem = InventoryItemRecord::find()->where(['purchasableId' => $this->duplicateOf->id])->one();
+                        if ($inventoryItem) {
+                            $inventoryItem->purchasableId = $canonicalPurchasableId;
+                            $inventoryItem->save();
+                            $this->inventoryItemId = $inventoryItem->id;
+                        }
+                    } else {
+                        // Set the inventory item data
+                        /** @var InventoryItemRecord|null $inventoryItem */
+                        $inventoryItem = InventoryItemRecord::find()->where(['purchasableId' => $canonicalPurchasableId])->one();
+                        if (!$inventoryItem) {
+                            $inventoryItem = new InventoryItemRecord();
+                            $inventoryItem->purchasableId = $canonicalPurchasableId;
+                            $inventoryItem->countryCodeOfOrigin = '';
+                            $inventoryItem->administrativeAreaCodeOfOrigin = '';
+                            $inventoryItem->harmonizedSystemCode = '';
+                            $inventoryItem->save();
+                            $this->inventoryItemId = $inventoryItem->id;
+                        }
                     }
                 }
             }
@@ -1076,6 +1111,7 @@ public function afterSave(bool $isNew): void
                     $purchasableStoreRecord->basePromotionalPrice = null;
                     $purchasableStoreRecord->stock = Plugin::getInstance()->getInventory()->getInventoryLevelsForPurchasable($this)->sum('availableTotal');
                     $purchasableStoreRecord->inventoryTracked = false;
+                    $purchasableStoreRecord->allowOutOfStockPurchases = false;
                     $purchasableStoreRecord->minQty = null;
                     $purchasableStoreRecord->maxQty = null;
                     $purchasableStoreRecord->promotable = false;
@@ -1096,6 +1132,7 @@ public function afterSave(bool $isNew): void
                             $purchasableStoreRecord->basePromotionalPrice = $purchasableStoreRecordDuplicate->basePromotionalPrice;
                             $purchasableStoreRecord->stock = Plugin::getInstance()->getInventory()->getInventoryLevelsForPurchasable($this)->sum('availableTotal');
                             $purchasableStoreRecord->inventoryTracked = $purchasableStoreRecordDuplicate->inventoryTracked;
+                            $purchasableStoreRecord->allowOutOfStockPurchases = $purchasableStoreRecordDuplicate->allowOutOfStockPurchases;
                             $purchasableStoreRecord->minQty = $purchasableStoreRecordDuplicate->minQty;
                             $purchasableStoreRecord->maxQty = $purchasableStoreRecordDuplicate->maxQty;
                             $purchasableStoreRecord->promotable = $purchasableStoreRecordDuplicate->promotable;
@@ -1111,7 +1148,8 @@ public function afterSave(bool $isNew): void
                 $purchasableStoreRecord->basePrice = $this->basePrice;
                 $purchasableStoreRecord->basePromotionalPrice = $this->basePromotionalPrice;
                 $purchasableStoreRecord->stock = Plugin::getInstance()->getInventory()->getInventoryLevelsForPurchasable($this)->sum('availableTotal');
-                $purchasableStoreRecord->inventoryTracked = $this->inventoryTracked;
+                $purchasableStoreRecord->inventoryTracked = $this::hasInventory() ? $this->inventoryTracked : false;
+                $purchasableStoreRecord->allowOutOfStockPurchases = $this->allowOutOfStockPurchases;
                 $purchasableStoreRecord->minQty = $this->minQty;
                 $purchasableStoreRecord->maxQty = $this->maxQty;
                 $purchasableStoreRecord->promotable = $this->promotable;
@@ -1317,7 +1355,7 @@ protected function attributeHtml(string $attribute): string
             'height' => $this->height !== null ? Craft::$app->getFormattingLocale()->getFormatter()->asDecimal($this->$attribute) . ' ' . Plugin::getInstance()->getSettings()->dimensionUnits : '',
             'minQty' => (string)$this->minQty,
             'maxQty' => (string)$this->maxQty,
-            'stock' => $stock,
+            'stock' => $this::hasInventory() ? $stock : '',
             'dimensions' => !empty($dimensions) ? implode(' x ', $dimensions) . ' ' . Plugin::getInstance()->getSettings()->dimensionUnits : '',
             default => parent::attributeHtml($attribute),
         };
@@ -1356,6 +1394,15 @@ protected static function defineDefaultTableAttributes(string $source): array
         ];
     }
 
+    /**
+     * @return bool
+     * @since 5.3.0
+     */
+    public static function hasInventory(): bool
+    {
+        return true;
+    }
+
     /**
      * @inheritdoc
      */
diff --git a/src/elements/Donation.php b/src/elements/Donation.php
index 20653b4a7b..f625933c1a 100644
--- a/src/elements/Donation.php
+++ b/src/elements/Donation.php
@@ -33,10 +33,24 @@
 class Donation extends Purchasable
 {
     /**
-     * @var bool Is the product available for purchase.
+     * By default the donation is not available for purchase.
+     *
+     * @inerhitdoc
      */
     public bool $availableForPurchase = false;
 
+
+    /**
+     * @inheritdoc
+     */
+    public static function hasInventory(): bool
+    {
+        return false;
+    }
+
+    /**
+     * @inheritdoc
+     */
     public function behaviors(): array
     {
         $behaviors = parent::behaviors();
@@ -50,6 +64,9 @@ public function behaviors(): array
         return $behaviors;
     }
 
+    /**
+     * @inheritdoc
+     */
     protected function defineRules(): array
     {
         $rules = parent::defineRules();
@@ -271,6 +288,7 @@ public function afterSave(bool $isNew): void
                 $purchasableStoreRecord->basePromotionalPrice = null;
                 $purchasableStoreRecord->stock = null;
                 $purchasableStoreRecord->inventoryTracked = false;
+                $purchasableStoreRecord->allowOutOfStockPurchases = false;
                 $purchasableStoreRecord->minQty = null;
                 $purchasableStoreRecord->maxQty = null;
                 $purchasableStoreRecord->promotable = false;
diff --git a/src/elements/conditions/products/ProductVariantStockConditionRule.php b/src/elements/conditions/products/ProductVariantStockConditionRule.php
index a049c08b94..0cb9bd5183 100644
--- a/src/elements/conditions/products/ProductVariantStockConditionRule.php
+++ b/src/elements/conditions/products/ProductVariantStockConditionRule.php
@@ -63,6 +63,10 @@ public function matchElement(ElementInterface $element): bool
     {
         /** @var Variant $variant */
         foreach ($element->getVariants() as $variant) {
+            if (!$variant::hasInventory()) {
+                return true;
+            }
+
             if ($variant->inventoryTracked === true && $this->matchValue($variant->getStock())) {
                 // Skip out early if we have a match
                 return true;
diff --git a/src/elements/db/PurchasableQuery.php b/src/elements/db/PurchasableQuery.php
index bbda2206c6..e9223aff60 100755
--- a/src/elements/db/PurchasableQuery.php
+++ b/src/elements/db/PurchasableQuery.php
@@ -695,6 +695,7 @@ protected function beforePrepare(): bool
             'purchasables_stores.maxQty',
             'purchasables_stores.minQty',
             'purchasables_stores.inventoryTracked',
+            'purchasables_stores.allowOutOfStockPurchases',
             'purchasables_stores.promotable',
             'purchasables_stores.shippingCategoryId',
             'subquery.price',
diff --git a/src/events/PurchasableOutOfStockPurchasesAllowedEvent.php b/src/events/PurchasableOutOfStockPurchasesAllowedEvent.php
new file mode 100644
index 0000000000..5b24e97113
--- /dev/null
+++ b/src/events/PurchasableOutOfStockPurchasesAllowedEvent.php
@@ -0,0 +1,42 @@
+<?php
+/**
+ * @link https://craftcms.com/
+ * @copyright Copyright (c) Pixel & Tonic, Inc.
+ * @license https://craftcms.github.io/license/
+ */
+
+namespace craft\commerce\events;
+
+use craft\commerce\base\PurchasableInterface;
+use craft\commerce\elements\Order;
+use craft\elements\User;
+use yii\base\Event;
+
+/**
+ * Class PurchasableOutOfStockPurchasesAllowedEvent
+ *
+ * @author Pixel & Tonic, Inc. <support@pixelandtonic.com>
+ * @since 5.3.0
+ */
+class PurchasableOutOfStockPurchasesAllowedEvent extends Event
+{
+    /**
+     * @var Order|null The order element.
+     */
+    public ?Order $order = null;
+
+    /**
+     * @var PurchasableInterface The purchasable element.
+     */
+    public PurchasableInterface $purchasable;
+
+    /**
+     * @var User|null The user performing the check.
+     */
+    public ?User $currentUser = null;
+
+    /**
+     * @var bool Is this purchasable available to be purchased when out of stock
+     */
+    public bool $outOfStockPurchasesAllowed = false;
+}
diff --git a/src/fieldlayoutelements/PurchasableStockField.php b/src/fieldlayoutelements/PurchasableStockField.php
index eeb28f0b8d..b9e7f8d369 100644
--- a/src/fieldlayoutelements/PurchasableStockField.php
+++ b/src/fieldlayoutelements/PurchasableStockField.php
@@ -207,10 +207,21 @@ public function inputHtml(ElementInterface $element = null, bool $static = false
             'disabled' => $static,
         ];
 
+        $storeAllowOutOfStockPurchasesLightswitchConfig = [
+            'label' => Craft::t('commerce', 'Allow out of stock purchases'),
+            'id' => 'store-backorder-allowed',
+            'name' => 'allowOutOfStockPurchases',
+            'small' => true,
+            'on' => $element->getIsOutOfStockPurchasingAllowed(),
+            'disabled' => $static,
+        ];
+
+
         return Html::beginTag('div') .
                 Cp::lightswitchHtml($storeInventoryTrackedLightswitchConfig) .
                 Html::beginTag('div', ['id' => $inventoryItemTrackedId, 'class' => 'hidden']) .
                     $inventoryLevelsTable .
+                    Cp::lightswitchFieldHtml($storeAllowOutOfStockPurchasesLightswitchConfig) .
                 Html::endTag('div') .
             Html::endTag('div');
     }
diff --git a/src/migrations/Install.php b/src/migrations/Install.php
index 756520a8ec..11042e331d 100644
--- a/src/migrations/Install.php
+++ b/src/migrations/Install.php
@@ -701,6 +701,7 @@ public function createTables(): void
             'availableForPurchase' => $this->boolean()->notNull()->defaultValue(true),
             'freeShipping' => $this->boolean()->notNull()->defaultValue(true),
             'inventoryTracked' => $this->boolean()->notNull()->defaultValue(true),
+            'allowOutOfStockPurchases' => $this->boolean()->notNull()->defaultValue(false),
             'stock' => $this->integer(), // This is a summary value used for searching and sorting
             'tracked' => $this->boolean()->notNull()->defaultValue(false),
             'minQty' => $this->integer(),
diff --git a/src/migrations/m241219_071723_add_inventory_backorder.php b/src/migrations/m241219_071723_add_inventory_backorder.php
new file mode 100644
index 0000000000..ed36f697e9
--- /dev/null
+++ b/src/migrations/m241219_071723_add_inventory_backorder.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace craft\commerce\migrations;
+
+use craft\commerce\db\Table;
+use craft\db\Migration;
+
+/**
+ * m241219_071723_add_inventory_backorder migration.
+ */
+class m241219_071723_add_inventory_backorder extends Migration
+{
+    /**
+     * @inheritdoc
+     */
+    public function safeUp(): bool
+    {
+        if (!$this->db->columnExists(Table::PURCHASABLES_STORES, 'allowOutOfStockPurchases')) {
+            $this->addColumn(Table::PURCHASABLES_STORES, 'allowOutOfStockPurchases', $this->boolean()->after('inventoryTracked')->notNull()->defaultValue(false));
+        }
+
+        return true;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function safeDown(): bool
+    {
+        echo "m241219_071723_add_inventory_backorder cannot be reverted.\n";
+        return false;
+    }
+}
diff --git a/src/migrations/m241220_082900_remove_inventory_for_non_inventory_purchasables.php b/src/migrations/m241220_082900_remove_inventory_for_non_inventory_purchasables.php
new file mode 100644
index 0000000000..8926ae77ca
--- /dev/null
+++ b/src/migrations/m241220_082900_remove_inventory_for_non_inventory_purchasables.php
@@ -0,0 +1,46 @@
+<?php
+
+namespace craft\commerce\migrations;
+
+use craft\commerce\db\Table;
+use craft\commerce\elements\Donation;
+use craft\db\Migration;
+use craft\db\Table as CraftTable;
+
+/**
+ * m241220_082900_remove_inventory_for_non_inventory_purchasables migration.
+ */
+class m241220_082900_remove_inventory_for_non_inventory_purchasables extends Migration
+{
+    /**
+     * @inheritdoc
+     */
+    public function safeUp(): bool
+    {
+        $purchasables = (new \craft\db\Query())
+            ->select(['items.id AS id', 'elements.type AS type'])
+            ->from(['items' => Table::INVENTORYITEMS])
+            ->leftJoin(['elements' => CraftTable::ELEMENTS], '[[items.purchasableId]] = [[elements.id]]')
+            ->all();
+
+        // Only remove the donation inventory items that shouldn't be there, can do others later.
+        foreach ($purchasables as $purchasable) {
+            if (is_subclass_of($purchasable['type'], Donation::class)) {
+                if (!$purchasable['type']::hasInventory()) { // should always be false, but just in case
+                    $this->delete(Table::INVENTORYITEMS, ['id' => $purchasable['id']]);
+                }
+            }
+        }
+
+        return true;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function safeDown(): bool
+    {
+        echo "m241220_082900_remove_inventory_for_non_inventory_purchasables cannot be reverted.\n";
+        return false;
+    }
+}
diff --git a/src/models/PurchasableStore.php b/src/models/PurchasableStore.php
index bfd81b6a77..4fa267b968 100644
--- a/src/models/PurchasableStore.php
+++ b/src/models/PurchasableStore.php
@@ -72,6 +72,12 @@ class PurchasableStore extends Model
      */
     public bool $availableForPurchase = false;
 
+    /**
+     * @var bool
+     * @since 5.3.0
+     */
+    public bool $allowOutOfStockPurchases = false;
+
     /**
      * @var bool
      */
@@ -91,7 +97,7 @@ protected function defineRules(): array
         $rules[] = [['purchasableId', 'storeId'], 'required'];
         $rules[] = [['purchasableId', 'storeId', 'stock', 'minQty', 'maxQty'], 'integer'];
         $rules[] = [['basePrice', 'basePromotionalPrice'], 'number'];
-        $rules[] = [['hasUnlimitedStock', 'promotable', 'availableForPurchase', 'freeShipping'], 'boolean'];
+        $rules[] = [['hasUnlimitedStock', 'promotable', 'availableForPurchase', 'freeShipping', 'allowOutOfStockPurchases'], 'boolean'];
         $rules[] = [['shippingCategoryId'], 'safe'];
 
         return $rules;
diff --git a/src/records/PurchasableStore.php b/src/records/PurchasableStore.php
index be51185f71..696d70fa25 100644
--- a/src/records/PurchasableStore.php
+++ b/src/records/PurchasableStore.php
@@ -22,6 +22,7 @@
  * @property float|null $basePromotionalPrice
  * @property int|null $stock
  * @property bool $inventoryTracked
+ * @property bool $allowOutOfStockPurchases
  * @property int|null $minQty
  * @property int|null $maxQty
  * @property bool $promotable
diff --git a/src/services/Inventory.php b/src/services/Inventory.php
index 5ce7ebb9fd..d486c40da4 100644
--- a/src/services/Inventory.php
+++ b/src/services/Inventory.php
@@ -690,6 +690,11 @@ public function orderCompleteHandler(Order $order)
 
             $purchasable = $lineItem->getPurchasable();
             // Don't reduce stock of unlimited items.
+
+            if (!$purchasable::hasInventory()) {
+                continue;
+            }
+
             if ($purchasable->inventoryTracked) {
                 if (!isset($qtyLineItem[$purchasable->id])) {
                     $qtyLineItem[$purchasable->id] = 0;
diff --git a/src/services/Purchasables.php b/src/services/Purchasables.php
index accb6d512d..aa09e36885 100644
--- a/src/services/Purchasables.php
+++ b/src/services/Purchasables.php
@@ -15,6 +15,7 @@
 use craft\commerce\elements\Order;
 use craft\commerce\elements\Variant;
 use craft\commerce\events\PurchasableAvailableEvent;
+use craft\commerce\events\PurchasableOutOfStockPurchasesAllowedEvent;
 use craft\commerce\events\PurchasableShippableEvent;
 use craft\commerce\Plugin;
 use craft\elements\User;
@@ -35,6 +36,31 @@
  */
 class Purchasables extends Component
 {
+    /**
+     * @event PurchasableAllowOutOfStockPurchasesEvent The event that is triggered when checking if the purchasable can be purchased when out of stock.
+     *
+     * This example allows users of a certain group to purchase out of stock items.
+     *
+     * ```php
+     * use craft\commerce\events\PurchasableAvailableEvent;
+     * use craft\commerce\services\Purchasables;
+     * use yii\base\Event;
+     *
+     * Event::on(
+     *     Purchasables::class,
+     *     Purchasables::EVENT_PURCHASABLE_ALLOW_OUT_OF_STOCK_PURCHASES,
+     *     function(PurchasableAllowOutOfStockPurchasesEvent $event) {
+     *         if($order && $user = $order->getUser()){
+     *            if($user->isInGroup(1)){
+     *                $event->outOfStockPurchasesAllowed = true;
+     *            }
+     *         }
+     *     }
+     * );
+     * ```
+     */
+    public const EVENT_PURCHASABLE_OUT_OF_STOCK_PURCHASES_ALLOWED = 'allowOutOfStockPurchases';
+
     /**
      * @event PurchasableAvailableEvent The event that is triggered when the availability of a purchasables is checked.
      *
@@ -109,6 +135,32 @@ class Purchasables extends Component
      */
     private ?Collection $_purchasableById = null;
 
+
+    /**
+     * @param PurchasableInterface $purchasable
+     * @param Order|null $order
+     * @param User|null $currentUser
+     * @return bool
+     * @throws Throwable
+     * @since 5.3.0
+     */
+    public function isPurchasableOutOfStockPurchasingAllowed(PurchasableInterface $purchasable, Order $order = null, User $currentUser = null): bool
+    {
+        if ($currentUser === null) {
+            $currentUser = Craft::$app->getUser()->getIdentity();
+        }
+
+        $outOfStockPurchasesAllowed = $purchasable->getIsOutOfStockPurchasingAllowed();
+
+        $event = new PurchasableOutOfStockPurchasesAllowedEvent(compact('order', 'purchasable', 'currentUser', 'outOfStockPurchasesAllowed'));
+
+        if ($this->hasEventHandlers(self::EVENT_PURCHASABLE_OUT_OF_STOCK_PURCHASES_ALLOWED)) {
+            $this->trigger(self::EVENT_PURCHASABLE_OUT_OF_STOCK_PURCHASES_ALLOWED, $event);
+        }
+
+        return $event->outOfStockPurchasesAllowed;
+    }
+
     /**
      * @param Order|null $order
      * @param User|null $currentUser
diff --git a/src/services/ShippingCategories.php b/src/services/ShippingCategories.php
index 4931c23f78..5c8a553cb0 100644
--- a/src/services/ShippingCategories.php
+++ b/src/services/ShippingCategories.php
@@ -108,7 +108,9 @@ public function getAllShippingCategoriesAsList(?int $storeId = null): array
      */
     public function getShippingCategoryById(int $shippingCategoryId, ?int $storeId = null): ?ShippingCategory
     {
-        return $this->getAllShippingCategories($storeId)->firstWhere('id', $shippingCategoryId);
+        $shippingCategories = $this->getAllShippingCategories($storeId);
+        $first = $shippingCategories->firstWhere('id', $shippingCategoryId);
+        return $first;
     }
 
     /**
diff --git a/src/translations/en/commerce.php b/src/translations/en/commerce.php
index 5c018323ad..4efbd8d387 100644
--- a/src/translations/en/commerce.php
+++ b/src/translations/en/commerce.php
@@ -56,6 +56,7 @@
     'Allow Checkout Without Payment' => 'Allow Checkout Without Payment',
     'Allow Empty Cart On Checkout' => 'Allow Empty Cart On Checkout',
     'Allow Partial Payment On Checkout' => 'Allow Partial Payment On Checkout',
+    'Allow out of stock purchases' => 'Allow out of stock purchases',
     'Allow' => 'Allow',
     'Allowed Qty' => 'Allowed Qty',
     'Alternative Phone' => 'Alternative Phone',