Why do some terrorist organizations choose not to—or fail to—kill? Of the 395 terrorist organizations operating between 1998 and 2005 only 39% had actually killed anyone. What factors account for this outcome? This article examines a series of organizational factors, including ideology, capability, and “home-base” country context, that the literature suggests are related to the decision to “go lethal.” We then test six hypotheses using data from the Memorial Institute for the Prevention of Terrorism (MIPT). Our statistical modeling suggests that ideology, capabilities, and “dilettantism” explain a significant proportion of the variation in whether an organization chooses to kill or not to kill. Leftists, anarchists, and environmentalists are far less likely to kill than those organizations inspired by religious ideologies. Larger organizations and those with more alliance ties are more likely to kill, while others are too “dilatory” and unserious about the “terrorist enterprise” to become lethal.