Many times in your ASP.NET applications, you need to interact with the local file system, directory structures, reading and writing to files. or performing many other tasks. The System.IO namespace in the .NET framework makes working with file system and directories very easy. However there are things you need to keep in mind that is security. When you reading, or writing a file or folders in Web application, you are actually executing on behalf of the users that being assigned to your web application and mostly it is under ASP.NET user or Network Service user. You need to make sure that the user itself has write or read access for the particular file or directory you are working on. In this article, I will list down few important classes in .NET that you need to know in order to manipulate files and folders in ASP.NET application.