Born on 31 May 1912 in Liuho (near Shanghai), China, Chien-Shiung Wu was one of the leading experimental physicists of the 20th century. Wu’s father operated one of the few primary schools at the time to admit girls, which allowed Wu to get a good education. She got a degree in physics from National Central University in Nanjing and then earned her PhD at the University of California, Berkeley. She joined Columbia University in 1944 to work on enriching uranium ore for the Manhattan Project. After the war she focused on creating experiments to precisely measure beta decay, a form of radioactivity in which a proton turns into a neutron, or vice versa, and emits a beta particle—an electron or a positron. After confirming physicist Enrico Fermi’s theory of beta decay, Wu set up an experiment to observe the beta emission of cobalt-60. She observed that the beta particles had a preferred direction of emission. Wu had proven that the process violates parity, the principle that for any particle interaction one cannot distinguish right from left or clockwise from counterclockwise. The 1957 discovery confirmed a theory by Tsung-Dao Lee and Chen Ning Yang, who were awarded the Nobel Prize in Physics later that year; Wu did not get recognized by the Nobel committee for her experimental triumph. In later years Wu studied the structure of hemoglobin, became the first woman to serve as president of the American Physical Society, and was awarded the Wolf Prize and the National Medal of Science. She died in 1997 at age 84; the Physics Today obituary was written by Lee and Richard Garwin. (Photo credit: AIP Emilio Segrè Visual Archives, Physics Today Collection)