This Physics Today article about Henri Becquerel and the discovery of radioactivity offers a glimpse into the world of experimental physics in 1896. The article begins with short biography of Henri Becquerel and the development of photography in the mid-1800s laboratories. Badash shows how the physicist discovered radioactivity over a period of months, guided by strong results from luminescence experiments with uranium salts. The author then explains Becquerel’s discovery of uranium rays and how the photographic images spurred science research worldwide. The article conveys how little the world knew about the atom in 1895, and how explosively research began to unravel its mysteries. Descriptions of Becquerel’s experiments are given, as are a number of pictures.