In this post I'm going to explain what are cookies and how to use them as a part of the ASP.NET client side state management. A cookie is a piece of data that is saved in the client web browser. The cookie is saved either in the memory of the web browser or as a text file in the file system of the client. Cookies are used to identify a user, to store state information, preferences of the user and etc. The ASP.NET use the cookies mechanism to track users session.