ASP.NET is a web application framework developed and maintained by Microsoft. It is a part of the .NET platform and is used to build dynamic web pages and web applications.

ASP.NET allows developers to create web applications using various programming languages such as C#, VB.NET, and F#. It provides a rich set of libraries and tools to simplify web development and is widely used for building enterprise-level applications.

ASP.NET supports a wide range of features such as server controls, caching, security, state management, and authentication. It also provides support for various data access technologies such as ADO.NET and Entity Framework.

ASP.NET can be hosted on various web servers such as IIS, Apache, and Nginx. It can also be used to build web applications for different platforms such as Windows, Linux, and macOS.

In recent years, ASP.NET has been evolving rapidly with the introduction of .NET Core, which is a cross-platform and open-source version of the framework. This has made ASP.NET more flexible and accessible to developers.