diff --git a/README.md b/README.md
index 8ebfe60..9cc7d12 100644
--- a/README.md
+++ b/README.md
@@ -4,6 +4,8 @@ Go Dependency Injection with Generics
 
 ## Example
 
+### Struct
+
 configuration.go
 
 ```go
@@ -97,3 +99,125 @@ func main() {
 	println(msgService.Welcome())
 }
 ```
+
+### Interface
+
+message_service.go
+
+```go
+package main
+
+import "git.apihub24.de/admin/generic-di"
+
+func init() {
+	di.Injectable(newMessageService)
+}
+
+type IMessageService interface {
+	Welcome() string
+}
+
+type messageService struct {
+	greeter *Greeter
+}
+
+func NewMessageService() IMessageService {
+	return &messageService{
+		// here was the Greeter from greeter.go injected
+		greeter: di.Inject[*Greeter](),
+	}
+}
+
+func (ctx *messageService) Welcome() string {
+	return ctx.greeter.Greet()
+}
+```
+
+main.go
+
+```go
+package main
+
+import di "git.apihub24.de/admin/generic-di"
+
+func main() {
+	msgService := di.Inject[IMessageService]()
+	// prints the message "Hello, Markus"
+	println(msgService.Welcome())
+}
+```
+
+## Replace Instance
+
+services/message_service.go
+
+```go
+package services
+
+import "git.apihub24.de/admin/generic-di"
+
+func init() {
+	di.Injectable(newMessageService)
+}
+
+type IMessageService interface {
+	Welcome() string
+}
+
+type messageService struct {
+	greeter *Greeter
+}
+
+func NewMessageService() IMessageService {
+	return &messageService{
+		// here was the Greeter from greeter.go injected
+		greeter: di.Inject[*Greeter](),
+	}
+}
+
+func (ctx *messageService) Welcome() string {
+	return ctx.greeter.Greet()
+}
+```
+
+main.go
+
+```go
+package main
+
+import di "git.apihub24.de/admin/generic-di"
+
+func main() {
+	msgService := di.Inject[services.IMessageService]()
+	// prints the message "Hello, Markus"
+	println(msgService.Welcome())
+}
+```
+
+message_service_test.go
+
+```go
+package services_test
+
+func init() {
+	// replace the instance of IMessageService with the Mock
+	di.Replace(newMessageServiceMock)
+}
+
+type messageServiceMock struct {}
+
+func newMessageServiceMock() services.IMessageService {
+	return &messageServiceMock{}
+}
+
+func (svc *messageServiceMock) Welcome() string {
+	return "Hello, Mock"
+}
+
+func TestMessageServiceMocking(t *testing.T) {
+	service := di.Inject[services.IMessageService]()
+	if service.Welcome() != "Hello, Mock" {
+		t.Errorf("expect Hello, Mock but get %s", service.Welcome())
+	}
+}
+```
diff --git a/injector.go b/injector.go
index 66265dd..feaaabb 100644
--- a/injector.go
+++ b/injector.go
@@ -21,6 +21,22 @@ func Injectable[T any](creator func() T) {
 	}
 }
 
+func Replace[T any](creator func() T, identifier ...string) {
+	Injectable(creator)
+	selector := getSelector[T]()
+	instanceSelector := getSelector[T](identifier...)
+	cre, creatorExists := creators[selector]
+	if !creatorExists {
+		return
+	}
+	createdInstance, instanceCreated := cre().(T)
+	if instanceCreated {
+		instanceMutex.Lock()
+		defer instanceMutex.Unlock()
+		instances[instanceSelector] = createdInstance
+	}
+}
+
 // Inject gets or create a Instance of the Struct used the Injectable constructor Function
 func Inject[T any](identifier ...string) T {
 	var nilResult T
diff --git a/injector_test.go b/injector_test.go
index af90237..dc8710c 100644
--- a/injector_test.go
+++ b/injector_test.go
@@ -13,6 +13,7 @@ func init() {
 	di.Injectable(newMessageService)
 	di.Injectable(newConfiguration)
 	di.Injectable(newGreetingService)
+	di.Injectable(newBasicOverridableService)
 }
 
 type (
@@ -30,8 +31,33 @@ type (
 		Greeting() string
 		TakeID() string
 	}
+
+	overridableService interface {
+		GetInstanceID() string
+		GetValue() string
+	}
+
+	basicOverridableService struct {
+		id string
+	}
+
+	basicOverridableServiceMock struct {
+		id string
+	}
 )
 
+func newBasicOverridableService() overridableService {
+	return &basicOverridableService{
+		id: uuid.NewString(),
+	}
+}
+
+func newBasicOverridableServiceMock() overridableService {
+	return &basicOverridableServiceMock{
+		id: uuid.NewString(),
+	}
+}
+
 func newConfiguration() *configuration {
 	return &configuration{}
 }
@@ -53,6 +79,22 @@ func newMessageService() *messageService {
 	}
 }
 
+func (ctx *basicOverridableService) GetInstanceID() string {
+	return ctx.id
+}
+
+func (ctx *basicOverridableService) GetValue() string {
+	return "i am original"
+}
+
+func (ctx *basicOverridableServiceMock) GetInstanceID() string {
+	return ctx.id
+}
+
+func (ctx *basicOverridableServiceMock) GetValue() string {
+	return "i am mock"
+}
+
 func (ctx *configuration) GetUserName() string {
 	return "Markus"
 }
@@ -134,6 +176,22 @@ func TestTryInterface_MultipleInstances(t *testing.T) {
 	}
 }
 
+func TestOverwriteInjectable(t *testing.T) {
+	basic := di.Inject[overridableService]()
+	basicID := basic.GetInstanceID()
+	if basic.GetValue() != "i am original" {
+		t.Errorf("wrong service instance get")
+	}
+	di.Replace(newBasicOverridableServiceMock)
+	basic = di.Inject[overridableService]()
+	if basic.GetInstanceID() == basicID {
+		t.Errorf("basic and newOne are the same instance")
+	}
+	if basic.GetValue() != "i am mock" {
+		t.Errorf("service not overwritten")
+	}
+}
+
 func TestDestroy(t *testing.T) {
 	_ = di.Inject[textService]("a")
 	di.Destroy[textService]("a")