From the CHM: “Enterprise Library consists of a collection of application blocks and core infrastructure. All of these are reusable software components designed to assist developers with common enterprise development challenges.

Enterprise Library also provides many highly configurable features that make it much easier to manage repetitive tasks, known as crosscutting concerns, which occur in many places in your applications. These include tasks such as logging, validation, caching, exception management, and more. In addition, the dependency injection container it provides can help to simplify and decouple your designs, make them more testable and understandable, and help you to produce more efficient designs and implementations of all kinds of applications.”

This diagram shows the blocks and their dependencies:

A first look at the new config tool:

For more info: http://blogs.msdn.com/agile/archive/2010/04/20/microsoft-enterprise-library-5-0-released.aspx