The physicist Lise Meitner (1878-1968) and the chemist Otto Hahn (1879-1968) worked together for over 30 years since 1907, spending the longest time at the Kaiser Wilhelm Institute for Chemistry in Berlin. Together and individually, they made numerous significant discoveries in physics, chemistry, and geology, and were, alongside the Curies, perhaps the most creative research duo of the 20th century. Following the discovery and radiochemical confirmation of nuclear fission by Otto Hahn and Fritz Strassmann in December 1938, Lise Meitner and Otto Robert Frisch provided the first physical explanation of this epoch-making event, which would lay the foundation for the atomic age and change the world. This book summarizes evidence of the deep friendship between Otto Hahn and Lise Meitner until their deaths: memories and letters from Lise Meitner, as well as tributes she wrote about her esteemed colleague.