The protests that began in Tunisia in December 2010, and quickly spread across the Arab world, have drawn significant attention to the impact of militaries and coercive institutions on protests and revolutionary movements. The actions of the militaries were a central determinant of the outcomes of the uprisings of 2010–2011. In Tunisia and Egypt the decision by military leaders to abstain from using force on mass protests to suppress them led to the downfall of the countries’ autocrats. In Syria and Bahrain, militaries defended political leaders with brutal force. In Yemen and Libya, militaries fractured, with some units remaining allied to the leader and using force on his behalf and others defecting. In still other states, leaders and militaries were able to forestall the emergence of large, regime-threatening protests.To explain these divergent outcomes, scholars and analysts have looked to a variety of explanatory factors. These focus on the attributes of the militaries involved, their civil-military relations, the size and social composition of the protests, the nature of the regime’s institutions, and the impact of monarchical traditions. These explanations offer many useful insights, but several issues remain under-studied. These include the impact of authoritarian learning and diffusion on protest trajectory. They also include the endogeneity of the protests to the nature of a country’s civil-military relations (i.e., how preexisting patterns of civil-military relations affected the possibility that incipient demonstrations would escalate to mass protests). Scholars also have been understandably captivated by the aforementioned pattern of military defection-loyalty, focusing on explaining that observed difference at the expense of studying other dependent variables. The next generation of scholarship on the uprisings therefore would benefit from efforts to conceptualize and investigate different aspects of variation in military behavior.Overall, the first-generation literature has proved enormously useful and laid the foundation for a much richer understanding of military behavior and reactions to popular uprisings in the Arab world and beyond.