Difference between ASP.NET Web API and ASP.NET MVC

S.No	ASP.NET Web API	ASP.NET MVC
1	Purpose of ASP.NET Web API: To create full blown HTTP services with easy and simple way that returns only data not view. i.e., ASP.NET Web API is focused on making output of raw data easy. In the WebForms world, ASP.NET Web API would be equivalent to .asmx pages.	Purpose of ASP.NET MVC: To create web applications that returns both views and data. i.e., ASP.NET MVC is focused on making output of HTML easy. In the WebForms world, ASP.NET MVC would be equivalent to .aspx pages.
2	Default Assumption for ASP.NET Web API: ASP.NET Web API by default assumes that primitive type comes from query string and non-primitive types comes from the form. It also assumes that we would only want to read the form body once, without caching, to have lower memory usage and better performance.	Default Assumption for ASP.NET MVC: ASP.NET MVC by default assumes user submitted data can come from multiple sources, be it in the query string or in the form.
3	Whether it is possible to make ASP.NET Web API output HTML ? Yes But, we need to do some additional work as provided below, Making additional classes to handle text/html during content negotiation in ASP.NET Web API.	Whether it is possible to make ASP.NET MVC output raw data ? Yes But, we need to do some additional work as provided below, Adding logic to handle OData queries in ASP.NET MVC.
4	GET AJAX Request in ASP.NET Web API: ASP.NET Web API allows GET AJAX request by default.	GET AJAX Request in ASP.NET MVC: GET AJAX request is blocked by ASP.NET MVC's JsonResult by default to prevent CSRF.
5	Whether RESTful services can be created with ASP.NET Web API ? ASP.NET Web API helps the creation of RESTful services over the .Net Framework.	Whether RESTful services can be created with ASP.NET MVC ? With ASP.NET MVC, we cannot able to create RESTful services.
6	Return format of data: ASP.NET Web API returns the data in various formats, such as JSON, XML and other format based on the accept header of the request.	Return format of data: ASP.NET MVC returns the data in the JSON format by using JSONResult.
7	Request Mapping: In ASP.NET Web API the request are mapped to the actions based on HTTP verbs.	Request Mapping: In ASP.NET MVC the request is mapped to actions name.
8	Where we can see the features such as: model binding, filters, routing etc., in ASP.NET Web API ? System.Web.Http	Where we can see the features such as: model binding, filters, routing etc., in ASP.NET MVC? System.Web.Mvc
9	Whether content negotiation and self hosting features are supported ? ASP.NET Web API supports content negotiation, self hosting. Content Negatiotion – It is about deciding the best response format data that could be acceptable by the client. it could be JSON,XML,ATOM or other formatted data	Whether content negotiation and self hosting features are supported ? ASP.NET MVC does not support content negotiation and self hosting features.
10	How routing is defined in ASP.NET Web API? Routing is defined by webapiconfig class i.e., using MapHttpRoute method. Unlike MVC, Routing API here does not use any reference to MVC .	How routing is defined in ASP.NET MVC? Routing is defined by routeconfig class i.e., using MapRoute method .
11	When to use ASP.NET Web API? Web API is more capable of supporting many different clients,namely, WPF Client, iPhone, Android, iPad, Windows Phone 7, Windows Phone 8, Web Browsers: IE, Firefox, Chrome etc., then ASP.NET Web API is likely going to be a better choice.	When to use ASP.NET MVC? Asp.NET MVC is optimized for having a web browser as a client. If our only client is a web browser, then MVC is likely going to be a better choice.

Note:

1.We can mix Web API and MVC controller in a single project to handle advanced AJAX requests which may return data in JSON, XML or any others format and building a full blown HTTP service. Typically, this will be called Web API self hosting.

2.When we have mixed MVC and Web API controller and you want to implement the authorization then we have to create two filters one for MVC and another for Web API since boths are different.