Ralph Marvin Steinman (January 14, 1943 – September 30, 2011) was a Canadian immunologist and cell biologist at Rockefeller University, who in 1973 coined the term dendritic cells while working as a postdoc in the lab of Zanvil A. Cohn, also at Rockefeller University. Steinman was one of the recipients of the 2011 Nobel Prize in Medicine.

Ralph Steinman was born into an Ashkenazi Jewish family in Montreal, one of four children of Irving Steinman (d. 1995) and Nettie Steinman (née Takefman, b. 1917). The family soon moved to Sherbrooke, where the father opened and ran a small clothing store "Mozart's". After graduating from Sherbrooke High School, Steinman moved back to Montreal where he stayed with his maternal grandparents Nathan and Eva Takefman. He received a Bachelor of Science degree from McGill University and received his M.D. (magna cum laude) in 1968 from Harvard Medical School. He completed his internship and residency at Massachusetts General Hospital.

On October 3, 2011, the Nobel Committee for Physiology or Medicine announced that he had received one-half of the Nobel Prize in Physiology or Medicine, for "his discovery of the dendritic cell and its role in adaptive immunity". The other half went to Bruce Beutler and Jules A. Hoffmann, for "their discoveries concerning the activation of innate immunity". However, the committee was not aware that he had died three days earlier, on September 30, from pancreatic cancer. This created a complication, since the statutes of the Nobel Foundation stipulate that the prize is not to be awarded posthumously. After deliberation, the committee decided that as the decision to award the prize "was made in good faith", it would remain unchanged.