Leo Kadanoff was an American physicist. He was a professor of physics at the University of Chicago and a former President of the American Physical Society (APS). He contributed to the fields of statistical physics, chaos theory, and theoretical condensed matter physics. He was born on January 14, 1937 in New York City, New York, United States. He has made important contributions to research in the properties of matter, the development of urban areas, statistical models of physical systems, and the development of chaos in simple mechanical and fluid systems. His best-known contribution was in the development of the concepts of "scale invariance" and "universality" as they are applied to phase transitions. More recently, he has been involved in the understanding of singularities in fluid flow. He was one of the recipients of the 1999 National Medal of Science, awarded by President Clinton. He is a member of the National Academy of Sciences and of the American Philosophical Society as well as being a Fellow of the American Physical Society and of the American Association for the Advancement of Science. He died on October 26, 2015 in Chicago, Illinois, United States.