Lindsay Helmholz (November 11, 1909 – March 17, 1993) was an American physicist who participated in the Manhattan Project during World War II that created the atomic bomb. He earned a PhD in chemistry at Johns Hopkins University before studying under Linus Pauling at California Institute of Technology and becoming a professor at Dartmouth College. After World War II, he joined the faculty at Washington University in St. Louis where he continued his work with X-ray diffraction and retired in 1978.