ASP.Net Web API is a framework that makes it easy to write RESTful applications. You can host WebAPI. The Web API can be hosted within an ASP.NET application or inside a separate process.  The workflow is something like this. The HttpServer receives the request messages and these are converted to an HttpRequestMessage. The message handlers process these messages. Custom handlers can be chained here. Handlers can be global or per route. The latter are configured along with the routes. If the message handler does not create a response on its own, the message continues through the pipeline to the controller. Since the controllers are found because they derive from a wellknown class or implement a well known Interface, the appropriate controller is instantiated and the corresponding action is selected. If the authorization fails, an error response is created and the rest of the pipeline is skipped. Next the model binding takes place and the OnActionExecuting and OnActionExecuted events are triggered before and after the action is invoked. The results are then converted through the handler and then the server.  Error responses and exceptions bypass the pipeline. In the model binding stage, the request message is used to create values for the parameters of the actions. These values are passed to the action when the action is invoked. Request Message is broken into Uri, Headers and entity body and these are converted by binders and value providers to simple type or by formatters to complex type. Model binders use the URI and the query string while the formatter reads the message body To convert the results, the return value from the action is checked. If the return type is HttpResponseMessage, it is passed through. If the return type is void, the response is created with status 204 ( no content ).  For all other return types, a media-type formatter serializes the value and writes it to the message body.