From DesigningPatterns

Background

.NET is a framework written by Microsoft mean to compete with the Java platform. While the Java Platform is meant to be platform agnostic, .NET is intended to be language agnostic (but tied to Windows).

Compatibility

• .NET compatibility with Windows versions
• .NET version 1.1/2.0 compatibility
• .NET 3.x is binary compatible with .NET 2.x, but .NET 3.x adds a number of new libraries and fixes a number of bugs (so a .NET 2.x/3.x application should be tested carefully on the other .NET version).