This document provides an overview of how to effectively use Twitter as a social media tool for libraries. It defines Twitter and reviews key Twitter terminology like hashtags and mentions. Statistics on Twitter's popularity and brief history are presented. Guidelines are given for setting up a library Twitter account, including tips for engaging followers through casual tone, avoiding jargon, responding quickly, and linking to library news/events. Suggested content includes author birthdays, quotes, programs, collections with the goal of connecting patrons and building social capital. Tracking and analytics tools are also reviewed.