ASP.NET is a Web application framework developed and marketed by Microsoft to allow programmers to build dynamic web sites, web applications and web services. It was first released in January 2002 with version 1.0 of the .NET Framework, and is the successor to Microsoft's Active Server Pages (ASP) technology. ASP.NET is built on the Common Language Runtime (CLR), allowing programmers to write ASP.NET code using any supported .NET language. The ASP.NET SOAP extension framework allows ASP.NET components to process SOAP messages.
Here are some point that gives the quick overview of ASP.NET.
1) Separation of Code from HTML
2) Support for compiled languages
3) Use services provided by the .NET Framework
4) Graphical Development Environment
5) State management
6) Update files while the server is running!
7) XML-Based Configuration Files