This book extends principal-agent theory to the case of pro-Russian rebel militias in Eastern Ukraine. Russia’s war in Ukraine demonstrates the much-discussed relations between the principal (Russia) and agent (rebel militias) in Eastern Ukraine. Russia’s aggression against Ukraine in 2014 was a frontal challenge to the post-Cold War European regional order, and since 2022 it has offered a challenge to the global order. Filling the gap in the literature on indirect warfare and insurgencies, this book offers systematic insights into structures and relations within the leaderless rebellion in the Donetsk and Luhansk Oblasts. It introduces the concept of the delegation of leaderless rebellion, based on the argument that it is a specific kind of rebellion when local elites do not actively participate as the leaders of the rebellion. Random people, without any fighting or political experience and with no social embeddedness, become rebel commanders, which means the principal – Russia – faces serious challenges but also benefits from opportunities to exercise complete control over the rebel forces and administration. This book will be of much interest to students of civil wars and insurgencies, political violence, Eastern European politics, and international relations in general.