This work includes biographical essays on 23 women who worked in atomic science during the first two decades of the 20th century, including Marie Curie, Lise Meitner, Irene Joliot-Curie, and a host of lesser-known women scientists whose life stories have never before been told. The biographies highlight the lives and work of these women, noting their contributions and the challenges they faced and overcame. Taken together the essays record their collective experiences, highlighting the support network that developed among them and the reasons women were more predominant in this field in the early part of this century than in other sciences. By recovering and recording individual and collective histories of the many eminent women in radioactivity whose work had a major impact on the scientific discoveries of the last century, a more complete, gender-integrated view of the history of this fascinating field emerges.