.NET LINQ (Language-Integrated Query)

language-integrated query to indicate that query is an integrated feature of the developer's primary programming languages (for example, Visual C#, Visual Basic). Language-integrated query allows query expressions to benefit from the rich metadata, compile-time syntax checking, static typing and IntelliSense that was previously available only to imperative code. Language-integrated query also allows a single general purpose declarative query facility to be applied to all in-memory information, not just information from external sources.
LINQ defines a set of general purpose standard query operators that allow traversal, filter, and projection operations to be expressed in a direct yet declarative way in any .NET-based programming language.
The extensibility of the query architecture is used in the LINQ project itself to provide implementations that work over both XML and SQL data. The query operators over XML (LINQ to XML) use an efficient, easy-to-use, in-memory XML facility to provide XPath/XQuery functionality in the host programming language.

SELECT, INSERT, UPDATE and DELETE data from SQL Server via LINQ query:

http://geekswithblogs.net/michelotti/archive/2007/12/30/118076.aspx

http://geekswithblogs.net/michelotti/archive/2007/12/30/118076.aspx

Download LINQ Project:
http://linqtosharepoint.codeplex.com/

http://www.codeproject.com/kb/vista/LINQ_1.aspx