Can we use multiple web.config files

One can work with more then one web.config file in asp.net, but only one web.config in each folder. 

On top of the every configuration files there will be a machine.config file which will have all system wide configuration settings.

You can find this file in your OS drive like C:/windows/Microsoft.NET/vFrameworkNumber/Config folder.

One can override those settings in web.config file from your application root folder. 

Same way you can add more web.config file in sub-folder and can override the setting of parent folder web.config file.