The ASPX file format is a text file format that is used to create Webform pages which means that it will often contain static HTML and other comands to define Web Controls and Web User Controls where the web site creator can place all of the static and dynamic content that is required for a given web page. Dynamic code that is run on a web server can also be placed within a block on the page which is similar to other techniques such as PHP and JSP.

It is recommended that the dynamic code for a web page be placed in a separate file. This is called the code-behind model. These files are typically named based on the ASPX file name but with an additional two letter extension. When this type of programming technique is used, the programmer with write code that corresponds to various different evens such as the page being loaded or a button on the page being clicked on. This is different from other programming which is a procedural walkthrough for the entire document.

The ASP.NET framework attempts to achieve greater performance over other similar technologies by compiling the server side code into very few DLL files on a web server. This will happen automatically the first time that a web page is requested, which means that the programmer will not have to compile each page separately. This offers ease of development that other scripting languages have as well as the performance benefits of a compiled binary. The only drawback to this technic is that it may cause a noticable delay to the internet user when a new web page is requested for the first time from the web server.

The ASPX file as well as any other required files are put in a virtual host on a compatible ASP.NET server. The first time that a page is requested, the .NET framework will compile the files and send the response. Any requests after this are served from the dll files. Developers can also precomile their pages before deployment which helps eliminate the need for compilation in a production environment that needs good performance.

There are also many other file formats that can be assocaiated to other versions of ASP.NET. Some of these include the ASAX, ASCX, ASHX and ASMX, however, there are many others as well.