James Cronin shared the Nobel Prize in physics in 1980 for showing that the laws of nature operate differently on matter and antimatter. Without this difference, no matter would exist in the universe at all. More recently, Cronin co-led the effort to build the Auger Observatory in Argentina. The Auger collaboration, consisting of 250 scientists from 16 countries, aims to track down the mysterious source of rare but extremely powerful cosmic rays that periodically bombard Earth. Cronin's honors include the National Medal of Science and election to the National Academy of Sciences and the Royal Society of London. He is the editor of Fermi Remembered, a book that documents the enduring significance of Enrico Fermi's life and work.