How do I find the .NET version used in an existing project?

I am expected to continue development on a C#/ASP.NET project that has changed hands multiple times, and no one person is sure which version of .NET is being used.

Is there something (perhaps an option in Project properties or elsewhere) that tells me which version of .NET the project uses?

EDIT :

The project's hosted on a remote server (an ancient one!) which runs on Windows Server 2003, and uses Visual Studio 2005. I checked the Web.config file, and under <system.web>, I found <compilation debug="true"> but no entry for targetFramework !
Does the existence of this entry depend on the .NET version too? Is this 2.x or older?

The tag in the project file is <TargetFrameworkVersion>v4.0</TargetFrameworkVersion>.

Alternatively under project properties:

If it is a web application, you can find it under Web.config: <compilation targetFramework="4.0">