The Oldstone Conference of 11 to 14 April 1949 was the third of three postwar conferences held to discuss quantum physics; arranged for the National Academy of Sciences by J. Robert Oppenheimer, who was again chairman. It followed the Shelter Island Conference of 1947 and the Pocono Conference of 1948. There were 24 participants; new participants were Robert F. Christy, Freeman Dyson, George Placzek, and Hideki Yukawa.