The present volume builds on the conference ‘Contingency in the Course of International Law: How International Law Could Have Been’, which we held in Amsterdam in the summer of 2018 under the auspices of the Amsterdam Center for International Law (ACIL). It was a sparkling event exceeding our expectations in substance and form; in the depth of the exchange; in open curiosity and intellectual rigour; and in sheer interest and numbers. We invited a few colleagues to the conference but wanted to seek out unfamiliar voices. About 140 scholars replied to our Call for Papers, and 60 presenters filled the conference. Fleur Johns opened the proceedings and Sam Moyn closed them. Both gave memorable keynote lectures that now, in revised versions, frame the present volume. We are truly grateful to all of the presenters and conference- participants for their engaged contributions and spirited exchanges, and to the contributors to the volume for their continued commitment, ongoing debate, and regular input.