Leonard Wayne Sumner is a Canadian philosopher notable for his work on normative and applied ethics, political philosophy, and the philosophy of law.

Sumner is currently Professor of Law and Philosophy at the University of Toronto, and, since 2002, University Professor, the highest academic honour that the university accords its faculty. Sumner received his doctoral degree from Princeton University in 1965, with a thesis supervised by Stuart Hampshire and Joel Feinberg. In 1990 he was elected a fellow of the Royal Society of Canada.