Andrew Marienhoff Sessler (December 11, 1928 – April 17, 2014) was an American physicist, academic (University of California, Berkeley), former director of the Lawrence Berkeley National Laboratory (1973–1980), humanitarian and former president (1998) of the American Physical Society.
Sessler was born in New York City in 1928. He was educated at Harvard University (B.A. in mathematics) and Columbia University (Ph.D. in physics) with dissertation Hyperfine structure of 3He. From 1954 to 1959, he was a member of the faculty at Ohio State University before moving to the Lawrence Berkeley National Laboratory where he served as Lab Director in 1973-80.
His areas of expertise were the physics of particle accelerators, particle physics and plasma physics. In addition to accelerator physics, he also published theoretical work on quantum-theoretical statistical mechanics, atomic physics and superfluidity. Sessler was also active in the study group of the National Academy of Sciences of the long-term effects of the atomic bombing of Hiroshima and Nagasaki, and in an initiative group of APS against landmines. Sessler was a member of the American Committee for Peace in Chechnya.