This book is about three things. First, it explores whether, why, and how states comply with international law, focusing on the United States and the factors that affect state calculations. Second, it examines the culture, structure, and processes of the State Department and their effect on the role of international law considerations in shaping State Department decision-making. Finally, it investigates the effect of the Trump administration and its views about international law on the culture and processes of the State Department, as well as the likely effect of a similar administration in the future. To help address these questions, seventy-seven high-level former State Department officials were interviewed, as well as a handful of former high-level attorneys in the Office of the Legal Adviser.