Book excerpt: A comprehensive examination of American women scientists across the sciences throughout the 20th century, providing a rich historical context for understanding their achievements and the way they changed the practice of science. Much more than a "Who's Who," this exhaustive two-volume encyclopedia examines the significant achievements of 20th century American women across the sciences in light of the historical and cultural factors that affected their education, employment, and research opportunities. With coverage that includes a number of scientists working today, the encyclopedia shows just how much the sciences have evolved as a professional option for women, from the dawn of the 20th century to the present. American Women of Science since 1900 focuses on 500 of the 20th century's most notable American women scientists—many overlooked, undervalued, or simply not well known. In addition, it offers individual features on 50 different scientific disciplines (Women in Astronomy, etc.), as well as essays on balancing career and family, girls and science education, and other sociocultural topics. Readers will encounter some extraordinary scientific minds at work, getting a sense of the obstacles they faced as the scientific community faced the questions of feminism and gender confronting the nation as a whole.