ASP.NET is a web application framework developed and marketed by Microsoft to allow programmers to build dynamic web sites, web applications and web services ASP.NET is a programming framework used to create enterprise-class Web Applications. These applications are accessible on a global basis leading to efficient information management. A unified Web development model ASP.NET includes the services necessary for you to build enterprise-class Web applications with a minimum of coding. It is a Web server technology for dynamically rendering HTML pages using a combination of HTML, Javascript, CSS, and server-side logic. ASP.NET can be used to create anything from small, personal websites through to large, enterprise-class web applications. ASP.NET is not just the next version of ASP; it is the next era of web development. ASP.NET allows you to use a full featured programming language such as C# (pronounced C-Sharp) or VB.NET to build web applications easily.

Unlike ASP, ASP.NET uses the Common Language Runtime (CLR) provided by the .NET Framework. This CLR manages execution of the code we write. ASP.NET code is a compiled CLR code instead of interpreted code (ASP). CLR also allows objects written in different languages to interact with each other. The CLR makes developement of Web applications simple.

ASP.NET Features

Easy Programming Model
ASP.NET makes building real world Web applications dramatically easier. Displaying data, validating user input, and uploading files are all extremely easy.
ASP.NET pages work in all browsers including Netscape, Opera, AOL, and Internet Explorer.
Flexible Language Options
ASP.NET lets you leverage your current programming language skills. ASP.NET supports more than 25 .NET languages (built-in support for VB.NET, C#, and JScript.NET), giving you unprecedented flexibility while choosing a language.
Great Tool Support
You can harness the full power of ASP.NET using any text editor, even Notepad. But Visual Studio .NET enhances the productivity of Visual Basic-style development to the Web. You can visually design ASP.NET Web Forms using drag-drop-double click techniques, and enjoy full-fledged code support including statement completion and color-coding. VS.NET also provides integrated support for debugging and deploying ASP.NET Web applications. The Enterprise versions of Visual Studio .NET deliver life-cycle features to help organizations plan, analyze, design, build, test, and coordinate teams that develop ASP.NET Web applications.

Rich Class Framework
Application features that used to be hard to implement, or required a 3rd-party component, can now be added in just a few lines of code using the .NET Framework. The .NET Framework offers over 4500 classes that include rich functionality like XML, data access, file upload, regular expressions, image generation, performance monitoring and logging, transactions, message queuing, SMTP mail, and much more. The improved Performance and Scalability ASP.NET lets you use serve more users with the same hardware.
Compiled execution
ASP.NET is much faster than classic ASP, while preserving the "just hit save" update model of ASP. However, no separate compile step is required. ASP.NET will automatically detect any changes, dynamically compile the files if needed, and store the compiled results to reuse for subsequent requests. Dynamic compilation ensures that your application is always up to date.

Rich output caching

ASP.NET output caching can dramatically improve the performance and scalability of your application. When output caching is enabled on a page, ASP.NET executes the page just once, and saves the result in memory in addition to sending it to the user. When another user requests the same page, ASP.NET serves the cached result from memory without re-executing the page. Output caching is configurable, and can be used to cache individual regions or an entire page. Output caching can dramatically improve the performance of data-driven pages by eliminating the need to query the database on every request.
Web-Farm Session State
ASP.NET session state lets you share session data user-specific state values across all machines in your Web farm. Now a user can hit different servers in the Web farm over multiple requests and still have full access to her session. And since business components created with the .NET Framework are free-threaded, you no longer need to worry about thread affinity.
Enhanced Reliability
ASP.NET ensures that your application is always available to your users.
Memory Leak, DeadLock and Crash Protection
ASP.NET automatically detects and recovers from errors like deadlocks and memory leaks to ensure your application is always available to your users. For example, say that your application has a small memory leak, and that after a week the leak has tied up a significant percentage of your server's virtual memory. ASP.NET will detect this condition, automatically start up another copy of the ASP.NET worker process, and direct all new requests to the new process. Once the old process has finished processing its pending requests, it is gracefully disposed and the leaked memory is released. Automatically, without administrator intervention or any interruption of service, ASP.NET has recovered from the error.
Easy Deployment
ASP.NET takes the pain out of deploying server applications. "No touch" application deployment. ASP.NET dramatically simplifies installation of your application. With ASP.NET, you can deploy an entire application as easily as an HTML page, just copy it to the server. No need to run regsvr32 to register any components, and configuration settings are stored in an XML file within the application.
Dynamic update of running application
ASP.NET now lets you update compiled components without restarting the web server. In the past with classic COM components, the developer would have to restart the web server each time he deployed an update. With ASP.NET, you simply copy the component over the existing DLL, ASP.NET will automatically detect the change and start using the new code.
Easy Migration Path
You don't have to migrate your existing applications to start using ASP.NET. ASP.NET runs on IIS side-by-side with classic ASP on Windows 2000 and Windows XP platforms. Your existing ASP applications continue to be processed by ASP.DLL, while new ASP.NET pages are processed by the new ASP.NET engine. You can migrate application by application, or single pages. And ASP.NET even lets you continue to use your existing classic COM business components.
XML Web Services
XML Web services allow applications to communicate and share data over the Internet, regardless of operating system or programming language. ASP.NET makes exposing and calling XML Web Services simple. Any class can be converted into an XML Web Service with just a few lines of code, and can be called by any SOAP client. Likewise, ASP.NET makes it incredibly easy to call XML Web Services from your application. No knowledge of networking, XML, or SOAP is required.
Mobile Web Device Support
ASP.NET Mobile Controls let you easily target cell phones, PDAs and over 80 mobile Web devices. You write your application just once, and the mobile controls automatically generate WAP/WML, HTML, or iMode as required by the requesting device.

Conclusion

NET platform has a lot to offer the software developer, including an ecumenical type system, better type information, and an efficient compilation model, all of which tighten up the various components. It provides you with better control over the front-end user experience. It has several improvements for the source-focused developer and puts you, the developer, in control of your HTML markup and code