Generics in the .NET Framework Class Library (C# Programming Guide)
Version 2.0 of the .NET Framework class library provides a new namespace, System.Collections.Generic, which includes several ready-to-use generic collection classes and associated interfaces. Other namespaces such as System also provide new generic interfaces such as IComparable<T>. These classes and interfaces are more efficient and type-safe than the non-generic collection classes provided in earlier releases of the .NET Framework. Before designing and implementing your own custom collection classes, consider whether you can use or derive a class from one of the classes provided in the base class library.
See Also
Reference
Introduction to Generics (C# Programming Guide)
Concepts
C# Programming Guide
When to Use Generic Collections