Lorraine Lois Foster (December 25, 1938, Culver City, California) is an American mathematician. In 1964 she became the first woman to receive a Ph.D. in mathematics from California Institute of Technology. Her thesis advisor at Caltech was Olga Taussky-Todd.
Born Lorraine Lois Turnbull, she attended Occidental College where she majored in physics. She was admitted to Caltech after receiving a Woodrow Wilson Foundation fellowship. In 1964 she joined the faculty of California State University, Northridge. She works in number theory and the theory of mathematical symmetry. Her Erdős number is 2.