Margaret Elaine Hamilton (née Heafield; born August 17, 1936) is an American computer scientist. She directed the Software Engineering Division at the MIT Instrumentation Laboratory, where she led the development of the on-board flight software for NASA's Apollo Guidance Computer for the Apollo program. She later founded two software companies, Higher Order Software in 1976 and Hamilton Technologies in 1986, both in Cambridge, Massachusetts.

Hamilton has published more than 130 papers, proceedings, and reports, about sixty projects, and six major programs. She coined the term "software engineering", stating, "I began to use the term 'software engineering' to distinguish it from hardware and other kinds of engineering, yet treat each type of engineering as part of the overall systems engineering process."

On November 22, 2016, Hamilton received the Presidential Medal of Freedom from president Barack Obama for her work leading to the development of on-board flight software for NASA's Apollo Moon missions.

Margaret Elaine Heafield was born August 17, 1936, in Paoli, Indiana, to Kenneth Heafield and Ruth Esther Heafield (née Partington). The family later moved to Michigan, where Margaret graduated from Hancock High School in 1954.

She studied mathematics at the University of Michigan in 1955 before transferring to Earlham College, where her mother had been a student. She earned a BA in mathematics with a minor in philosophy in 1958. She cites Florence Long, the head of the math department at Earlham, as helping with her desire to pursue abstract mathematics and become a mathematics professor.

She says her poet father and headmaster grandfather inspired her to include a minor in philosophy in her studies.

In Boston, Hamilton initially intended to enroll in graduate study in abstract mathematics at Brandeis University. However, in mid-1959, Hamilton began working for Edward Norton Lorenz, in the meteorology department at Massachusetts Institute of Technology (MIT). She developed software for predicting weather, programming on the LGP-30 and the PDP-1 computers at Marvin Minsky's Project MAC. Her work contributed to Lorenz's future publications on chaos theory, as acknowledged by Lorenz himself. At the time, computer science and software engineering were not yet established disciplines; instead, programmers learned on the job with hands-on experience. She moved on to another project in the summer of 1961, and hired and trained Ellen Fetter as her replacement.

From 1961 to 1963, Hamilton worked on the Semi-Automatic Ground Environment (SAGE) Project at the MIT Lincoln Lab, where she was one of the programmers who wrote software for the prototype AN/FSQ-7 computer (the XD-1), used by the U.S. Air Force to search for possibly unfriendly aircraft. She also wrote software for a satellite tracking project at the Air Force Cambridge Research Laboratories. The SAGE Project was an extension of Project Whirlwind, started by MIT to create a computer system that could predict weather systems and track their movements using simulators. SAGE was soon developed for military use in anti-aircraft air defense. Hamilton said: