This book covers the first 35 years of nuclear physics, especially in the areas of radioactivity and radioactive emissions which were the main discoveries in nuclear physics during its first three decades. It follows the nuclear phenomena step by step, paying special attention to outstanding discoveries, such as Curie's discovery of radium, Rutherford-Soddy law, discovery of isotopes, and Rutherford's artificial transmutations. The author aims to present in a critical approach the growth of nuclear physics as seen by a nuclear physicist and historian.