LINQ to SQL is an O/RM (object relational mapping) implementation that ships in the .NET Framework "Orcas" release, and which allows you to model a relational database using .NET classes. You can then query the database using LINQ, as well as update/insert/delete data from it.
LINQ to SQL fully supports transactions, views, and stored procedures. It also provides an easy way to integrate data validation and business logic rules into your data model.
Developers can use LINQ with any data source. They can express efficient query behavior in their programming language of choice, optionally transform/shape data query results into whatever format they want, and then easily manipulate the results. LINQ-enabled languages can provide full type-safety and compile-time checking of query expressions, and development tools can provide full intellisense, debugging, and rich refactoring support when writing LINQ code.
LINQ supports a very rich extensibility model that facilitates the creation of very efficient domain-specific operators for data sources. The "Orcas" version of the .NET Framework ships with built-in libraries that enable LINQ support against Objects, XML, and Databases.
For More details about the LINQ :
Part 1: Introduction to LINQ to SQL
Part 2: Defining our Data Model Classes
Part 3: Querying our Database
Part 4: Updating our Database
Part 5: Binding UI using the ASP:LinqDataSource Control
Part 6: Retrieving Data Using Stored Procedures
Part 7: Updating our Database using Stored Procedures
Part 8: Executing Custom SQL Expressions
Part 9: LINQ to SQL (Part 9 - Using a Custom LINQ Expression with the