ASP.NET files, typically using the .aspx extension (the extension value we'll focus on), are web pages generated using Microsoft's ASP.NET framework. These files contain a combination of HTML markup, server-side code (usually C# or VB.NET), and ASP.NET controls. When a user requests an ASP.NET page, the server processes the code within the file, dynamically generating HTML that is then sent to the user's browser. This allows for creating dynamic and interactive web applications. The server-side code interacts with databases, performs calculations, and manipulates data before rendering the final HTML output. ASP.NET provides a rich set of features for building complex web applications, including state management, security, and data binding. The framework handles many of the complexities of web development, allowing developers to focus on the application's logic and user interface. ASP.NET pages are a core component of many enterprise-level web applications and websites.