Expression trees represent code in a tree-like data structure, where each node is an expression, for example, a method call or a binary operation such as x < y.
You can compile and run code represented by expression trees. This enables dynamic modification of executable code, the execution of LINQ queries in various databases, and the creation of dynamic queries. For more information about expression trees in LINQ, see How to: Use Expression Trees to Build Dynamic Queries (C# and Visual Basic) and Walkthrough: Creating an IQueryable LINQ Provider.
Expression trees are also used in the dynamic language runtime (DLR) to provide interoperability between dynamic languages and the .NET Framework and to enable compiler writers to emit expression trees instead of Microsoft intermediate language (MSIL). For more information about the DLR, see Dynamic Language Runtime Overview.
You can have the C# or Visual Basic compiler create an expression tree for you based on an anonymous lambda expression, or you can create expression trees manually by using the System.Linq.Expressions namespace.
