Can I use different programming languages in ASP.NET?
Multiple languages in use is called interoperability or "interop" for short. You can use different programming language for every page in ASP.NET web application. In ASP.NET you can mix together, say, C# and Visual Basic .NET in the same application, although not in the same page. Complete page must be written in the same language. One language - one .aspx file.
An ASP.NET page is restricted to code written in a single programming language. The default language is Visual Basic , but any other language can be declared as the default language for the page by placing a directive at the top of the page, such as the following:
Although only one language can be used on a single page , any user controls that you use on a page can be written in different languages, including Visual C++. This allows applications to take advantage of function libraries in different languages.
Using multiple languages in the same ASP.NET project is helpful in at least a couple of scenarios when you're integrating existing code and when you have developers on the project with different skills. All code inside App_Code folder must be written in one language. But, you can make sub folders inside App_Code folder and have different language in each folder.