Robert Stanley Breed (October 17, 1877 – February 10, 1956) was an American biologist, born in Brooklyn, Pennsylvania.
In 1902 he became professor of biology at Allegheny College and was there secretary of the faculty in 1907–1910.
He became known especially for his researches on the post-embryonic development of insects and for his contributions to scientific journals on the public milk supply.
From the 1920s until his death in 1956, he was a principal editor of Bergey's Manual of Determinative Bacteriology.
Breed died in 1956, and was buried at the Evergreen Cemetery in Brooklyn Township, Susquehanna County, Pennsylvania.