What determines the activity and lethality of militant groups? To answer this question, a two-step count method disentangles activity and lethality in terms of ideology, capacity, and environmental factors. A first step assesses the determinants of group activity, measured by the number of incidents in which a group was involved. The second step considers the number of fatalities, conditional on the number of incidents. Similar factors drive militant group activity and lethality, but some links are stronger than others. Specifically, ideological factors are particularly strong determinants of lethality; capacity and environmental factors matter more for activity.