Kirtley Fletcher Mather (February 13, 1888 – May 5, 1978) was an American geologist and faculty member at Harvard University. An expert on petroleum geology and mineralogy, Mather was a prominent scholar, advocate for academic freedom, social activist, and critic of McCarthyism. He is known for his efforts to harmonize the dialogue between science and religion, his role in the Scopes "Monkey Trial", his faith-based liberal activism, and his advocacy for adult education programs.