Why do some armed nonstate groups seek foreign volunteers while others do not? This article identifies four variables—political considerations, operational needs, organizational capacity, and ideational fit—that shape armed nonstate actors’ choices concerning foreign volunteers. The essay also presents an original theory for how these variables interact. It argues that while both operational and political considerations inform a group’s position on foreign volunteers, when the two conflict, political considerations take priority. In addition, organizational capacity determines a group’s ability to translate need into action, serving as a necessary (but insufficient) condition for foreign mobilization.