LINQ and the features that made it possible: lambdas, extension methods, var and anonymous types.

This release added 10 features, each with a before-and-after example.

Features in C# 3.0

• Anonymous types - Create objects without explicitly defining a type.
• Auto implemented properties - Declare properties without explicit backing fields.
• Collection initializers - Populate collections inline during construction.
• Expression trees - Represent code as data structures for analysis or transformation.
• Extension methods - Add methods to existing types without modifying them.
• Implicitly typed local variables - Declare variables with var so the compiler infers the type.
• Lambda expressions - Create inline functions using concise => arrow syntax.
• Object initializers - Set property values when creating an object.
• Partial methods - Define a method signature in a partial class for implementation elsewhere.
• Query expressions - Provide a native query syntax reminiscent of SQL.

Nearby versions

C# 4.0 and later · C# 2.0 and earlier