WCF Service Application vs WCF Service library
When you try to create a WCF Service using Visual Studio, you will see 2 kinds of WCF which maybe let you confused : WCF Service Application vs WCF Service library.
So which one you should select ?
Simple to say:
If you want your WCF services to be host to different platforms, ie: IIS/ASP.NET, Windows service, or even a console application, you should choose WCF Library, but you need to create host by yourself (in Visual Studio, the host file is .svc), you need to reference your library from your new host. If you only your Services host to IIS/ASP.NET , then select WCF Application maybe better.
Here is a good article about the difference (by Scott Marlowe):