.NET Framework 3.5:

The .NET Framework 3.5 introduces new features for the technologies in 2.0 and 3.0 and additional technologies in the form of new assemblies. LINQ (Language Integrated Query), ASP.NET AJAX and new compilers for c#, Visual Basic and C++ are the technologies introduced in the .NET Framework 3.5.
     .NET Framework 3.5 = Features of 3.0+ ADO.NET entity Framework + LINQ

Changes in 3.5 on comparison with 3.0:

•   New language features in C# 3.0 and VB.NET 9.0 compiler.

•   An anonymous type with static type inference was introduced.

•  Language Integrated Query (LINQ)  was introduced along with its various providers

·         LINQ to Objects

·         LINQ to XML

·         LINQ to SQL

•   Support for paging to ADO.NET was introduced.

•   Peer-to-peer networking stack, including a managed PNRP resolver.

•   Enhanced WCF and WF runtimes, which let WCF work with POX and JSON data, and also expose WF workflows as WCF services. WCF services can be made stateful using the WF persistence model.

•   Support for HTTP pipelining and syndication feeds.

•   ASP.NET AJAX is included.