Margaret Cairns Etter, known informally as Peggy Etter (12 September 1943 – 9 June 1992), was an American chemist who contributed to the development of solid state chemistry for crystalline organic compounds.
She is known for her work characterizing and classifying contacts by hydrogen bonds in organic compounds.
Her "enlightened imagination, innovative creativity, and unfailing enthusiasm" is recognised as having a "transformative effect" in many areas of organic chemistry.