Classical Greece has long been associated with the city-state, a system of independent entities that fought to maintain their autonomy in the face of external aggression. But the same historical period also witnessed the flourishing of more than ten regional cooperatives, or koina, whose city-state members were required to partially surrender local autonomy. How and why the koinon developed is the subject of Assistant Professor of History Emily Mackil’s States of Interaction: A Developmental History and Social Analysis of the Greek Koinon. Mackil analyzes literary, archaeological, epigraphic, and numismatic evidence for the koinon in order to address the nature of state power in the ancient world in a new way. Rather than focus exclusively on the conflicts surrounding these regional cooperatives, Mackil’s research reveals the extent to which koina enabled and protected cooperation between its members in a way that went beyond politics. Mackil argues that a sense of group (ethnic) identity both suggested and reinforced patterns of religious interaction between communities. These patterns suggested cooperation between the same communities in military undertakings and economic interaction. As these cooperative structures became institutionalized in a regional state, certain shared places of worship eventually became political meeting places. “States of Interaction” also brings to light ways in which the Greeks utilized state power to gain access to a greater diversity and extent of economic resources, an important institutional response to an ecological condition of extreme fragmentation and uneven distribution of natural resources.