The Microsoft Enterprise Library is a set of tools and programming libraries for the Microsoft .NET Framework. It provides APIs to facilitate proven practices in core areas of programming including data access, logging, exception handling and others. Enterprise Library is provided as pluggable binaries and source code, which can be freely used and customized by developers for their own purposes. It also ships with test cases and quickstarts.

Each application block addresses a specific cross-cutting concern and provides highly configurable features, which results in higher developer productivity. The Application Blocks in Enterprise Library are designed to be as agnostic as possible to the application architecture, for example the Logging Application Block may be used equally in a web, smart client or service-oriented application.

Microsoft has produced a number of other deliverables that leverage Enterprise Library Application Blocks, including the Web Service Software Factory and Smart Client Software Factory.^{[citation needed]}

In addition to the Application Blocks, the standard Microsoft distribution of the Enterprise Library includes:

There have been several versions of the Microsoft Enterprise Library:

Unity is the dependency injection component of Microsoft Enterprise Library, which grew out of the Dependency Injection Application Block. It later became a standalone library and continues to be maintained by the community. Version 3.5, released in April 2014, adds support for Xamarin.

Microsoft Enterprise Library 6 was released in April 2013. New features include:

This release has also retired the following 3 blocks: