This historical grounding brings into close contact two areas of study that have for much too long stood back-to-back: the English School of International Relations (ES), and International Political Economy (IPE). For the ES, the book fills in the large economic gap in its understanding and portrayal of the primary institutions of international society. Adding in the economic sector has a major impact on how the other primary institutions of international society both work in themselves, and interact with each other. For IPE, the book opens up a new and usefully detailed view of the constant and wide-ranging interaction of the market with the other social and political institutions of global international society. The approach through primary institutions fills in the middle ground between the big-picture classical approaches to IPE, and the current focus on intergovernmental organisations and regimes.