Significantly, two of the best known 20th-century American composers, both Brooklyn-born, did not meet each other on US soil. Aaron Copland and Roger Sesssions first met in Paris in 1924 at Nadia Boulanger's apartment. In 1926 a long correspondence began that lasted until the 1970s, but which was concentrated in the decade 1926-1936: of the 107 extant letters between them, fully ninety fall into this decade. Clearly, in 1936, a falling out occurred between the two composers; at the end of this article, I shall hazard a hypothesis as to why.