Joan Elaine Argetsinger Steitz (born January 26, 1941) is Sterling Professor of Molecular Biophysics and Biochemistry at Yale University and Investigator at the Howard Hughes Medical Institute.

In 1975, she published a research finding for which she is widely known, demonstrating that ribosomes use complementary base pairing to identify the start site on mRNA.

[14][15] In 1980, Steitz in collaboration with Michael Lerner published another critical paper, using immunoprecipitation with human antibodies from patients with autoimmunity to isolate and identify snRNPs (pronounced "snurps") and detect their role in splicing.

Steitz's paper "set the field ahead by light years and heralded the avalanche of small RNAs that have since been discovered to play a role in multiple steps in RNA biosynthesis," noted Susan Berget.

"[18] Steitz's research[19] may yield new insights into the diagnosis and treatment of autoimmune disorders such as lupus, which develop when patients make anti-nuclear antibodies against their own DNA, snRNPs, or ribosomes.

"[11] Steitz has served in numerous professional capacities, including as scientific director of the Jane Coffin Childs Memorial Fund for Medical Research (1991–2002) and as editorial board member of Genes & Development.

Her nomination for the Royal Society reads: Joan Steitz is one of the pioneers of the field of RNA biology who is world-renowned for her many seminal contributions.