It is a subset of the full .NET Framework 3.5 SP1 that targets client applications
It includes only client-specific assemblies (i.e. Win Forms, WPF, WCF, ClickOnce) and doesn’t contain any of the server-specific assemblies (i.e. LINQ To SQL, Windows Workflow Foundation)
The size of the .NET Framework Client Profile is 26 MB
A client machine that has the .NET Framework Client Profile cannot later upgrade to the full version of the .NET Framework if needed