This document provides an overview of the microblogging service Twitter. It explains that Twitter allows users to post short updates of 140 characters or less to share what they are currently doing. Users can follow friends on Twitter to see their updates and others can follow them to see their posts. The document outlines how to create an account and post tweets via various methods, and describes some common uses of Twitter like sharing news, events, conversations and humor. It also notes some potential problems with Twitter like distraction and loss of content if the service goes away.