This book traces the development of the international society tradition from its origins in Grotius' On the Law of War and Peace to its crystallization in Bull's The Anarchical Society. It follows the idea of sociability among peoples as it was presented by Grotius and substantiated by Pufendorf, through the skepticism of Voltaire and Kant, to emerge as humanitarian warfare and human rights in the international liberal movement, 'world society' in the 20th century Catholic revival, and common practices and social understandings in the English School in the period of disciplinary development in international relations after the Second World War. Cornelia Navari was Associate Professor of Political Science and International Studies at the University of Birmingham UK and Visiting Professor of International Affairs at the University of Buckingham. She has written Internationalism and the State in the 20th Century (2000) and Public Intellectuals and International Affairs (2012). Among edited works are Hans J Morgenthau and the American Experience (2018), International Organization in the Anarchical Society (2019) with Tonny Brems Knudsen, and International Society: The English School (2020). She was made an International Studies Association Distinguished Scholar in 2019.