An ASPX file is an Active Server Page Extended (ASPX) file, which is a webpage generated by web servers running the Microsoft ASP.NET framework. It contains one or more scripts written in VBScript or C# code that are processed by the web server into HTML, which is sent to the user's web browser. ASPX files are often written with Microsoft Visual Web Developer and designed for the Microsoft ASP.NET framework.

ASPX pages are also called ".NET Web forms." They can be identified in a web browser when the URL in the address field ends in ".aspx". ASP.NET was developed by Microsoft and released in 2002 to succeed Active Server Pages (ASP). It is a web application framework utilized by web developers to produce dynamic web sites and applications.