Web.config file is the main configuration options for a Web application in ASP.NET. The file is an XML document that defines configuration information regarding the web application. The web.config file contains information that controls the loading of modules, security settings, configurations session state, compiler options and the language of the application. The web.config files may also contain specific objects such as connection strings to the database. In our case include the use of global variables of the application, redefining the maximum size of requests, setting sessions and cookies, security permissions, assembled the app, redirects on error and modules. Note the use of RewriteModule module is explained in another section.