Introduction
LINQ is a feature of the programming languages C# and Microsoft Visual Basic .NET. Compilers are included with Visual Studio.
LINQ adds a SQL-like syntax and vocabulary to each of the languages, which can be used to query data sources. But unlike other languages and query syntaxes which vary from one type of data source to another, LINQ can be used to query, in principle, any data source whatsoever. For this reason, developers may find that it is the only query syntax that they ever need to know.
The LINQ to SharePoint Provider
The LINQ to SharePoint Provider is defined in the Microsoft.SharePoint.Linq namespace. It translates LINQ queries into Collaborative Application Markup Language (CAML) queries. It is no longer necessary for developers to know how to write CAML queries. LINQ queries can be used in server code.
The gateway class for the LINQ to SharePoint provider is Microsoft.SharePoint.Linq.DataContext which represents the data of a SharePoint Foundation Web site. It is parallel in use and function to the System.Data.Linq.DataContext class in the LINQ to SQL provider.