Gustav Mahler and Richard Strauss came to know one another as young conductors in Leipzig in 1887. From then until Mahler's death in 1911--the year of the first performance of Der Rosenkavalier--they kept in touch. Mahler himself described their relationship as that of two miners tunneling from opposite directions with the hope of eventually meeting. This publication of their correspondence, which includes twenty-five previously unknown Strauss letters, offers a portrait of two men who were as antithetical in their musical means and goals as in their temperaments and personalities, but who exercised a strong fascination for one another. These sixty-three letters show both composers advancing in their careers as they battled against adverse conditions in the musical world at the turn of the century. They present Mahler's energetic support of Strauss's Symphonia Domestica, which Mahler conducted in 1904 and, in turn, Strauss's championing of Mahler's music, especially the Second and Third Symphonies. The correspondence is fully annotated and is supplemented with a major essay by Herta Blaukopf.