C# Version 2.0 Specification
C# 2.0 introduces several language extensions, the most important of which are Generics, Anonymous Methods, Iterators, and Partial Types.
The language extensions in C# 2.0 were designed to ensure maximum compatibility with existing code. For example, even though C# 2.0 gives special meaning to the words where, yield, and partial in certain contexts, these words can still be used as identifiers. Indeed, C# 2.0 adds no new keywords as such keywords could conflict with identifiers in existing code.