The first Shelter Island Conference on the Foundations of Quantum Mechanics was held from June 2–4, 1947 at the Ram's Head Inn in Shelter Island, New York. Shelter Island was the first major opportunity since Pearl Harbor and the Manhattan Project for the leaders of the American physics community to gather after the war. As Julian Schwinger would later recall, "It was the first time that people who had all this physics pent up in them for five years could talk to each other without somebody peering over their shoulders and saying, 'Is this cleared?' "
The conference, which cost $850, was followed by the Pocono Conference of 1948 and the Oldstone Conference of 1949. They were arranged with the assistance of J. Robert Oppenheimer and the National Academy of Sciences. Later Oppenheimer deemed Shelter Island the most successful scientific meeting he had ever attended; and as Richard Feynman recalled to Jagdish Mehra in April 1970: "There have been many conferences in the world since, but I've never felt any to be as important as this. .... The Shelter Island Conference was my first conference with the big men. .... I had never gone to one like this in peacetime."
The conference was conceived by Duncan MacInnes, a scientist studying electrochemistry at the Rockefeller Institute for Medical Research. Once the president of the New York Academy of Sciences, MacInnes had already organized a number of small scientific conferences. However, he believed that the later conferences had suffered from a bloated attendance, and over this issue, he resigned from the Academy in January 1945. That fall, he approached the National Academy of Sciences (NAS) with the idea of a series of 2–3 day conferences limited to 20–25 people. Frank Jewett, the head of the NAS, liked the idea; he envisioned a "meeting at some quiet place where the men could live together intimately", possibly "at an inn somewhere", and suggested that MacInnes focus on a couple of pilot programs. MacInnes' first choice was "The Nature of Biopotentials", a subject close to his own heart; the second would be "The Postulates of Quantum Mechanics", which later became "Foundations of Quantum Mechanics".