Asp.net when do session variables expire

So how can i set the timeout of the session's variable unlimited until it is changed by program?Any suggestions? You can't set timeout value to unlimited. In my web app I'm using some session variables, which are set when I login: e.g. Session("user_id") = reader("user_id") I use this through my. In order to preserve server memory, questions implements a rolling timeout mechanism which discards the session information for a user if no request is seen.