This book joins the growing literature on identity and political community in international relations. Traditional explanations for the security relations between states focus on anarchy, power, and self-interest. In contrast, Cronin argues that elites can build security relations around "transnational communities" based on common identity and social cohesion; in turn, the type of community-based security arrangements created depends on the character and intensity of emerging political bonds. For example, the nineteenth-century Concert of Europe was built on mutual recognition and a shared view of the common good. Other security arrangements -- ranging from the Arab League and the British Commonwealth to NATO -- are organized around different combinations of shared ideologies, regime type, and regions. The book makes a strong case that durable cooperative security depends on political ties and common affinities between sovereign states -- an insight, for example, that the security debate in East Asia might consider. But it is less clear from Cronin's telling how these transnational communities emerge and how long they last in the face of crisis.