 <p>Actually, session and cookies are not always separate things. Often, but not always, session uses cookies.</p> <p>There are some good answers to your question in these other questions here. Since your question is specifically about saving the user's IDU (or ID), I don't think it is quite a duplicate of those other questions, but their answers should help you.</p> <p><a href="http://stackoverflow.com/questions/359434/cookies-vs-session">cookies vs session</a></p> <p><a href="http://stackoverflow.com/questions/553185/cache-vs-session-vs-cookies">Cache VS Session VS cookies?</a></p> <p><a href="http://stackoverflow.com/questions/623815/what-is-the-difference-between-a-session-and-a-cookie">What is the difference between a Session and a Cookie?</a></p>