public static void RegisterAsDependencyResolver(this Container container, HttpConfiguration configuration) { if (container == null) { throw new ArgumentNullException("Simple Injector Container"); } var resolver = new SimpleInjectionDependencyResolver { Container = container }; var httpResolver = new SimpleInjectionHttpDependencyResolver { Container = container }; DependencyResolver.SetResolver(resolver); //This is required for MVC configuration.DependencyResolver = httpResolver; //This is required for API }