diff --git a/CHANGELOG.md b/CHANGELOG.md
index ee7374e..f592121 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 5.1.0
+- Feature: Adds new flag `--join` for `mob start` to join an existing session
+  `mob start --join` (#437)
+
 # 5.0.1
 - Fix: The configuration option `MOB_SKIP_CI_PUSH_OPTION_ENABLED` now works correctly
 
diff --git a/configuration/configuration.go b/configuration/configuration.go
index 4c10f79..2533b1c 100644
--- a/configuration/configuration.go
+++ b/configuration/configuration.go
@@ -29,7 +29,8 @@ type Configuration struct {
 	NotifyMessage                  string // override with MOB_NOTIFY_MESSAGE
 	NextStay                       bool   // override with MOB_NEXT_STAY
 	StartIncludeUncommittedChanges bool
-	StartCreate                    bool   // override with MOB_START_CREATE variable
+	StartCreate                    bool // override with MOB_START_CREATE variable
+	StartJoin                      bool
 	StashName                      string // override with MOB_STASH_NAME
 	WipBranchQualifier             string // override with MOB_WIP_BRANCH_QUALIFIER
 	WipBranchQualifierSeparator    string // override with MOB_WIP_BRANCH_QUALIFIER_SEPARATOR
@@ -143,6 +144,8 @@ func ParseArgs(args []string, configuration Configuration) (command string, para
 			newConfiguration.DoneSquash = SquashWip
 		case "--create":
 			newConfiguration.StartCreate = true
+		case "--join", "-j":
+			newConfiguration.StartJoin = true
 		case "--delete-remote-wip-branch":
 			newConfiguration.ResetDeleteRemoteWipBranch = true
 		case "--room":
diff --git a/configuration/configuration_test.go b/configuration/configuration_test.go
index 844aec0..683f997 100644
--- a/configuration/configuration_test.go
+++ b/configuration/configuration_test.go
@@ -39,6 +39,26 @@ func TestParseArgsStartCreate(t *testing.T) {
 	test.Equals(t, true, configuration.StartCreate)
 }
 
+func TestParseArgsStartJoin(t *testing.T) {
+	configuration := GetDefaultConfiguration()
+
+	command, parameters, configuration := ParseArgs([]string{"mob", "start", "--join"}, configuration)
+
+	test.Equals(t, "start", command)
+	test.Equals(t, "", strings.Join(parameters, ""))
+	test.Equals(t, true, configuration.StartJoin)
+}
+
+func TestParseArgsStartJoinShort(t *testing.T) {
+	configuration := GetDefaultConfiguration()
+
+	command, parameters, configuration := ParseArgs([]string{"mob", "start", "-j"}, configuration)
+
+	test.Equals(t, "start", command)
+	test.Equals(t, "", strings.Join(parameters, ""))
+	test.Equals(t, true, configuration.StartJoin)
+}
+
 func TestParseArgsDoneNoSquash(t *testing.T) {
 	configuration := GetDefaultConfiguration()
 	test.Equals(t, Squash, configuration.DoneSquash)
diff --git a/help/help.go b/help/help.go
index 2b6c049..0a6c8dc 100644
--- a/help/help.go
+++ b/help/help.go
@@ -20,6 +20,7 @@ Basic Commands with Options:
     [--include-uncommitted-changes|-i]   Move uncommitted changes to wip branch
     [--branch|-b <branch-postfix>]       Set wip branch to 'mob/<base-branch>` + configuration.WipBranchQualifierSeparator + `<branch-postfix>'
     [--create]                           Create the remote branch
+	[--join|-j]                          Join existing wip branch
     [--room <room-name>]                 Set room name for timer.mob.sh once
   next
     [--stay|-s]                          Stay on wip branch (default)
diff --git a/mob.go b/mob.go
index 3834614..7adc4f5 100644
--- a/mob.go
+++ b/mob.go
@@ -538,6 +538,11 @@ func start(configuration config.Configuration) error {
 	git("fetch", configuration.RemoteName, "--prune")
 	currentBaseBranch, currentWipBranch := determineBranches(gitCurrentBranch(), gitBranches(), configuration)
 
+	if !currentWipBranch.hasRemoteBranch(configuration) && configuration.StartJoin {
+		say.Error("Remote wip branch " + currentWipBranch.remote(configuration).String() + " is missing")
+		return errors.New("remote wip branch is missing")
+	}
+
 	if !currentBaseBranch.hasRemoteBranch(configuration) && !configuration.StartCreate {
 		say.Error("Remote branch " + currentBaseBranch.remote(configuration).String() + " is missing")
 		say.Fix("To start and create the remote branch", "mob start --create")
diff --git a/mob_test.go b/mob_test.go
index 0252dd6..8a52992 100644
--- a/mob_test.go
+++ b/mob_test.go
@@ -390,6 +390,14 @@ func TestStartWithPushDefaultTracking(t *testing.T) {
 	assertMobSessionBranches(t, configuration, "mob-session")
 }
 
+func TestStartWithJoiningNonExistingSession(t *testing.T) {
+	_, configuration := setup(t)
+	assertOnBranch(t, "master")
+	configuration.StartJoin = true
+	start(configuration)
+	assertOnBranch(t, "master")
+}
+
 func TestReset(t *testing.T) {
 	output, configuration := setup(t)