The reference book is dedicated to LINQ (Language Integrated Query) technology, a new functionality of the C # language and the .NET Framework, which allows you to write secure structured queries to local object collections and remote data sources. The basic concepts of LINQ, such as deferred execution, iterator chains and type recognition in lambda expressions, the difference between local and interpreted queries, C # query syntax, comparison of query syntax with lambda syntax, as well as queries with mixed syntax, compiling complex queries, writing efficient LINQ queries for SQL, building expression trees, LINQ queries for XML.