Scholars of Latin American politics have been challenged to account for the varied outcomes of the transitions from authoritarian to democratic government that have occurred in many countries south of the border during the past two decades. What explains why some transitions were relatively smooth, with the military firmly in control of the process, while others witnessed substantial concessions by the military to civilian leaders, or even total military collapse? Rather than focus on causes external to the military, such as the previous legacy of democratic rule, severe economic crisis, or social protest, as other scholars have done, Craig Arceneaux draws attention to the important variables internal to the military, such as its unity or ability to coordinate strategy. Using this &"historical-institutionalist&" approach, he compares five different transitions in Brazil and three countries of the Southern Cone&—Argentina, Chile, and Uruguay&—to show what similarities and differences existed and how the differences may be attributed to variations in the internal institutional structure and operation of the military.