Thomas Arthur Steitz (August 23, 1940 – October 9, 2018) 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". Steitz also won the Gairdner International Award in 2007 "for his studies on the structure and function of the ribosome which showed that the peptidyl transferase (EC 2.3.2.12) was an RNA catalyzed reaction, and for revealing the mechanism of inhibition of this function by antibiotics".