In this paper, I provide an update on the Global Terrorism Database (GTD), an open source event database that now includes information on nearly 88,000 domestic and international terrorist attacks since 1970. I describe our original data collection efforts, some of the strategies we have employed to improve the quality and comprehensiveness of the data, and the strengths and weaknesses of open source data in general and the GTD in particular. I then provide descriptive statistics on the contents of the most recently available version of the GTD and offer observations about the future of event databases. While social and behavioral research on terrorism has expanded dramatically in recent years, theoretical perspectives that incorporate terrorism and the collection of valid data on terrorism have lagged behind other criminological specializations. Despite the enormous resources devoted to countering terrorism, we have surprisingly little empirical information about which strategies are most effective.