Conventional wisdom on proxy warfare exclusively focuses on explaining governments’ provision of military, logistical, and financial support to rebel groups involved in conflict abroad. In reality, foreign militant groups play a much larger role in these partnerships than recognized: foreign militants often provide government partners with intelligence, logistical support, access to their military infrastructure, and send elite units to train and supplement their state partner’s troops. Because armed non-state actors are smaller and face greater difficulties accessing resources, the fact that they provide any type of support – let alone deploying their forces to conduct joint combat operations with state armed forces abroad – is puzzling. In this presentation, I provide insights into the strategic benefits that foreign militants receive from supporting states, identify factors that influence the types of support foreign militants provide to government partners once the decision to provide support has been made, and highlight how foreign militants can constrain and influence their government partners’ future behavior. To do so, I conduct an in-depth examination of the overtime trends in the various types of support that Shia paramilitary groups from Lebanon, Iraq, Afghanistan, and Pakistan provided to the Syrian regime and Russian forces throughout the course of the decade-long Syrian conflict.