ASP.NET是由微软在.NET Framework框架中所提供，开发Web应用程序的类别库，封装在System.Web.dll文件中，显露出System.Web命名空间，并提供ASP.NET网页处理、扩充以及HTTP信道的应用程序与通信处理等工作，以及Web Service的基础架构。ASP.NET是ASP技术的后继者，但它的发展性要比ASP技术要强大许多。

ASP.NET可以运行在安装了.NET Framework的IIS服务器上，若要在非微软的平台上运行，则需要使用Mono平台，ASP.NET在2.0版本已经定型，在.NET Framework 3.5上则加上了许多功能，像是ASP.NET AJAX、ASP.NET MVC Framework、ASP.NET Dynamic Data与Microsoft Silverlight的服务器控件等。

ASP.NET is an open-source server-side web application framework designed for web development to produce dynamic web pages. It was developed 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.