Thomas Arthur Steitz (August 23, 1940 – October 9, 2018[1]) was an American biochemist, a Sterling Professor of Molecular Biophysics and Biochemistry at Yale University, and investigator at the Howard Hughes Medical Institute, best known for his pioneering work on the ribosome.

Steitz was awarded the 2009 Nobel Prize in Chemistry along with Venkatraman Ramakrishnan and Ada Yonath "for studies of the structure and function of the ribosome".

[5] He received a Ph.D. in biochemistry and molecular biology from Harvard University in 1966 where he worked under the direction of subsequent 1976 chemistry Nobel Prize winner William N. Lipscomb, Jr.

Steitz briefly held an assistant professorship at the University of California, Berkeley, but he resigned on the grounds that the institution would not accept his wife Joan into a faculty position because she was a woman.

Steitz and Peter Moore determined the atomic structure of the large 50S ribosomal subunit using X-ray crystallography, and published their findings in Science in 2000.