Sir Sidney Frederic Harmer FRS (9 March 1862 - 22 October 1950) was a British zoologist. He was President of the Linnean Society 1927-1931 and was awarded the Linnean Medal in 1934.
Sidney Harmer was Superintendent of the Cambridge University Museum of Zoology from 1892-1908. Harmer was Keeper of Zoology at the Natural History Museum from 1909 to 1921 and director of the Museum from 1919 to 1927. His research library is held in the National Marine Biological Library at the Marine Biological Association in Plymouth.
He was the father of Russell Harmer, the gold-medal winning British sailor, and great uncle of the actress and writer Juliet Harmer, best known for her role in the 1960s TV series Adam Adamant Lives!