Gerald Enoch Sacks (born 1933, Brooklyn) is a logician who holds a joint appointment at Harvard University as a Professor of Mathematical Logic and the Massachusetts Institute of Technology as a Professor Emeritus. His most important contributions have been in recursion theory. Named after him is Sacks forcing, a forcing notion based on perfect sets and the Sacks Density Theorem, which asserts that the partial order of the recursively enumerable Turing degrees is dense.
Sacks earned his Ph.D. in 1961 from Cornell University under the direction of J. Barkley Rosser, with a dissertation entitled On Suborderings of Degrees of Recursive Insolvability. Among his notable students are Lenore Blum, Harvey Friedman, Sy Friedman, Leo Harrington, Richard Shore, and Theodore Slaman.
- Degrees of unsolvability, Princeton University Press 1963, 1966
- Saturated Model Theory, Benjamin 1972; 2nd edition, World Scientific 2010
- Higher Recursion theory, Springer 1990
- Selected Logic Papers, World Scientific 1999
- Mathematical Logic in the 20th Century, World Scientific 2003