This book explores the foundations and evolution of modern corporate fiduciary law in the United States and the United Kingdom. Today US and UK fiduciary law provide very different approaches to the regulation of directorial behaviour. However, as the book shows, the law in both jurisdictions borrowed from the same sources in eighteenth- and nineteenth-century English fiduciary and commercial law. The book identifies the shared legal foundations and authorities and explores the drivers of corporate fiduciary law’s contemporary divergence. In so doing it challenges the prevailing accounts of corporate legal change and stability in the US and the UK.