This work features the classified lectures that galvanized the Manhattan Project scientists - with annotations for the nonspecialist reader and an introduction by a Pulitzer Prize-winning historian. In March 1943 a group of young scientists, sequestered on a mesa near Santa Fe, attended a crash course in the new atomic physics. The lecturer was Robert Serber, J. Robert Oppenheimer's protege, and they learned that their job was to invent the world's first atomic bomb. Serber's lecture notes, nicknamed the "Los Alamos Primer", were mimeographed and passed from hand to hand, remaining classified for many years. They are published here for the first time, and now contemporary readers can see just how much was known and how terrifyingly much was unknown when the Manhattan Project began. Could this 'gadget', based on the newly discovered principles of nuclear fission, really be designed and built? Could it be small enough and light enough for an airplane to carry? If it could be built, could it be controlled? Working with Richard Rhodes, Pulitzer Prize-winning historian of the development of the atomic bomb, Professor Serber has annotated original lecture notes with explanations of the physics terms for the nonspecialist. His preface, an informal memoir, vividly conveys the mingled excitement, uncertainty, and intensity felt by the Manhattan Project scientists. Rhodes' introduction provides a brief history of the development of atomic physics up to the day that Serber stood before his blackboard at Los Alamos. In this edition, "The Los Alamos Primer" finally emerges from the archives to give a new understanding of the very beginning of nuclear weapons. No seminar anywhere has had greater historical consequences.