This Cambridge Companion explores the main senses of the term 'international arbitration'; including the arbitration of private commercial disputes, disputes between a State and a foreign investor, disputes between States and also between a State and its parts. It treats these various forms as being inter-related, if not always conceptually, then as a matter of history, rather than as collective victims of imprecise language. The book touches not only on current debates but also more foundational aspects, such as the tension between party autonomy and State authority, and the pacifist roots of modern international arbitration. Thus, it aims to offer a concise survey of the history, the main issues as well as the latest developments in a single, handy volume. It will be an invaluable introduction to the subject for students studying international arbitration, commercial law and international law, and also lawyers and the general reader.