The using keyword has two major uses:

• As a directive, when it is used to create an alias for a namespace or to import types defined in other namespaces. See using Directive.

• As a statement, when it defines a scope at the end of which an object will be disposed. See using Statement.

 See Also

Reference

C# Keywords
Namespace Keywords (C# Reference)
extern (C# Reference)

Concepts

C# Programming Guide
Namespaces (C# Programming Guide)

Other Resources

C# Reference