Bernstein’s relationship with Aaron Copland was one of the most significant of his life. Starting with their first meeting in 1937, this chapter considers Copland’s musical influence on Bernstein as an emerging composer and the support and opportunities Copland provided during Bernstein’s formative years. It then goes on to explore the importance of Bernstein’s Copland advocacy on the conducting podium, with reference to major commissions, concerts, and recordings. Drawing on both their public and private comments and correspondence, the changing nature of their relationship and views on each other’s activities are traced, resulting in a shared portrait of more than five decades of friendship and musical connections.