WCF - Windows Communication Foundation(WCF) has been created by Microsoft with .NET Framework 3.0. It supports SOAP BASED services. It has compatibility with HTTP, TCP, UDP, ETC. Good for developing secure and interoperable services. Used for back end purposes.

WEB API - Web API open SOURCE framework. It has compatibility with HTTP only. It has a support for non-SOAP based services. It is very light weight hence good for developing services for low bandwidth devices. It supports OData. It supports most of the MVC features. Used for front end purposes.

WCF - Windows Communication Foundation(WCF) has been created by Microsoft with .NET Framework 3.0. It supports SOAP based services. It has compatibility with HTTP, TCP, UDP, etc. Good for developing secure and interoperable services. Used for back end purposes.

WEB API - Web API open source framework. It has compatibility with HTTP only. It has a support for non-SOAP based services. It is very light weight hence good for developing services for low bandwidth devices. It supports OData. It supports most of the MVC features. Used for front end purposes.