This book presents the complete history of the Los Alamos Laboratory from its founding, through the completion of the first atomic bomb, to the end of the laboratory's control by the Manhattan District in December 1946. The book is divided into two parts treating the periods before and after the end of World War II in August, 1945. The organizational divisions at Los Alamos covered in the book include administration, theoretical, weapons physics, chemistry and metallurgy, research, explosives, and ordnance. The book includes graphs, photographs, several appendices and a glossary. It is the second volume of an 11 volume series on the history of physics.