The subject of the book is a biography of the theoretical physicist Arnold Sommerfeld (1868-1951). Although Sommerfeld is famous as a quantum theorist for the elaboration of the semi-classical atomic theory (Bohr-Sommerfeld model, Sommerfeld's fine-structure constant), his role in the history of modern physics is not confined to atoms and quanta. Sommerfeld left his mark in the history of mathematics, fluid mechanics, a number of physical subdisciplines and, in particular, as founder of a most productive "school" (Peter Debye, Wolfgang Pauli, Werner Heisenberg, Linus Pauling and Hans Bethe were his pupils, to name only the Nobel laureates among them). This biography is to a large extent