This book provides a comprehensive account of how the Louisiana Purchase of 1803 was financed. Where existing research has focused predominantly on the political and diplomatic significance of the Purchase, this book demonstrates the importance of the Purchase to global financial history. The book provides context and background for the Louisiana Purchase and examines the role of key actors and companies, focusing particularly on the 'forgotten financiers' of the Purchase - individuals from the US, France and the UK including Alexander Baring, Albert Gallatin, Pierre Cesar Labouchere and Francois Barbe-Marbois. Based on extensive, original archival research, the chapters will illuminate the role played by these individuals in bringing about financial innovation and facilitating a major transaction that doubled the size of the original United States and helped set the country on a path to global power. The book will be a valuable resource for historians of Europe and America, particularly those with interests in economic and financial history, as well as banking and finance scholars who are interested in the emergence of large-scale international finance in the 19th century.