In autumn of 1949, Enrico Fermi returned to Italy after an eleven-year absence to deliver nine lectures, six in Rome and three in Milan.They were addressed to the young Italian physicists and to a more general audience only then beginning to recover from the physical and moral disruption of the war. This volume represents the first time that these nine lectures have been published in English. Published in collaboration with the Italian Physical Society (SIF), the book includes a presentation of the president of SIF, an introduction written by the editors, and two substantial essays: one on Fermi’s life, and a second on Fermi’s skill in talking about Physics in a clear and sparkling manner.