This document analyzes a dataset of over 37 billion tweets spanning 2006 to 2013 to study the evolution of Twitter users and their behavior. It finds that the percentage of U.S. and Canadian users dropped from over 80% to 32% as Twitter spread globally, and that the percentage of tweets in English fell from 83% to 52%. It also observes increases in tweet deletions, inactive accounts, and suspended accounts, as well as a shift from desktop to mobile usage, with over half of tweets now coming from mobile devices. The results provide insight into how Twitter and user behavior have changed over time.