Some rebel groups abuse noncombatant populations, while others exhibit restraint. Insurgent leaders in some countries transform local structures of government, while others simply extract resources for their own benefit. In some contexts, groups kill their victims selectively, while in other environments violence appears indiscriminate, even random. This book presents a theory that accounts for the different strategies pursued by rebel groups in civil war, explaining why patterns of insurgent violence vary so much across conflicts. It does so by examining the membership, structure, and behavior of four insurgent movements in Uganda, Mozambique, and Peru. Drawing on interviews with nearly 200 combatants and civilians who experienced violence firsthand, it shows that rebels' strategies depend in important ways on how difficult it is to launch a rebellion. The book thus demonstrates how characteristics of the environment in which rebellions emerge constrain rebel organization and shape the patterns of violence that civilians experience.