LINQ, Language INtegrated Query, is a new extension to the Visual Basic and C# programming languages designed to simplify data queries and database interaction. It addreses O/R mapping issues by making query operations like SQL statements part of the programming language. Adding to its power, LINQ is extensible and can be used to query various data sources. It offers built-in support for querying in-memory collections like arrays or lists, XML, DataSets, and relational databases. LINQ in Action is a fast-paced, comprehensive tutorial for professional developers who want to use LINQ. This book explores what can be done with LINQ, shows you how it works in an application, and addresses the emerging best practices. It presents the general purpose query facilities offered by LINQ in the upcoming C# 3.0 and VB.NET 9.0 languages. A running example introduces basic LINQ concepts. You ll then learn to query unstructured data using LINQ to XML and relational data with LINQ to SQL. Finally, you ll see how to extend LINQ for custom applications. LINQ in Action will guide you along as you navigate this new world of lambda expressions, query operators, and expression trees. You ll also explore the new features of C# 3.0, VB.NET 9.0. The book is very practical, anchoring each new idea with running code. You will discover all the basics needed to get a clear understanding of LINQ. Whether you want to use LINQ to query objects, XML documents, or relational databases, you will find all the information you need to get started. But LINQ in Action does not stop at the basic code. This book also shows you how LINQ can be used for advanced processing of data. This includes coverage of LINQ s extensibility, which allows querying more data sources than those supported by default. All code samples are built on a concrete business case. The running example, LinqBooks, is a personal book cataloging system that shows you how to create LINQ applications with Visual Studio 2008.