Margaret J. Geller (born December 8, 1947) is an American astrophysicist at the Harvard–Smithsonian Center for Astrophysics. Her work has included pioneering maps of the nearby universe, studies of the relationship between galaxies and their environment, and the development and application of methods for measuring the distribution of matter in the universe. Geller made pioneering maps of large-scale structure in the universe. Geller received a Bachelor of Arts degree in Physics at the University of California, Berkeley (1970) and a Ph.D. in Physics from Princeton (1974). Geller completed her doctoral dissertation, titled "Bright galaxies in rich clusters: a statistical model for magnitude distributions", under the supervision of James Peebles Although Geller was thinking about studying solid state physics in graduate school, Charles Kittel suggested she go to Princeton to study astrophysics. After research fellowships at the Harvard–Smithsonian Center for Astrophysics and the Institute of Astronomy in Cambridge, England, she became an assistant professor of Astronomy at Harvard University (1980-1983). She then joined the permanent scientific staff of the Smithsonian Astrophysical Observatory, a partner in the Harvard-Smithsonian Center for Astrophysics. Geller is a Fellow of the American Association for the Advancement of Science and a Fellow of the American Physical Society. In 1990, she was elected as a Fellow of the American Academy of Arts and Sciences. Two years later, she was elected to the Physics section of the US National Academy of Sciences. From 2000 to 2003, she served on the Council of the National Academy of Sciences. She has received seven honorary degrees (D. S. H. C. or L. H. C.). Geller is known for observational and theoretical work in cosmology and extragalactic astronomy. Her long range goals are to discover what the universe looks like and to understand how the patterns we observe today evolved. In the 1980s, she made pioneering maps of the nearby universe, which included the Great Wall^[8] and was the inspiration for Jasper Johns 2020 piece called Slice. Her SHELS project maps the distribution of dark matter in the universe. With the 6.5-m MMT, she leads a deeper survey of the middle-aged universe called HectoMAP. Geller has developed innovative techniques for investigating the structure and mass of clusters of galaxies and the relationship between clusters and their surroundings. Geller is also a co-discoverer of hypervelocity stars which may be an important tracer of the matter distribution in the Galaxy.