REST is a concept of exchanging data on HTTP generally in the form of XML/JSON.
http://en.wikipedia.org/wiki/Representational_state_transfer
Microsoft introduced inbuilt WCF REST support from Framework 3.5.
Have a look at below links for more information on WCF REST.
http://msdn.microsoft.com/en-us/netframework/dd547388
http://msdn.microsoft.com/en-us/netframework/cc950529
However you can develop REST service even without using WCF REST Project template of Visual Studio.
Below CodeProject article demonstrates how you can develop REST service using a simple
HttpHandler.
Developing a REST Web Service using C# - A walkthrough
Support for
JSON format in WCF RST is available from Framework 3.5 and above. In the attributes of your Web/REST Method you can assign value of
RequestFormat
Property to
WebMessageFormat.Json
.
Edited - Spelling corrections.