The collections for which the Pierpont Morgan Library was known for much of the last century - early printed books, fine bindings, master drawings, ancient Near Eastern seals and tablets, and illuminated, literary, and historical manuscripts - began with its founder, Pierpont Morgan. Absent from these so-called paper collections are, with a few noteworthy exceptions, music manuscripts and letters. Thanks to two substantial gifts and a long-term loan, the Morgan Library's music manuscript holdings are today among the finest in the world. In 1968 the trustees of the Mary Flagler Cary Charitable Trust gave the library Mrs. Cary's outstanding collection of music manuscripts and letters; in 1977 the Heineman Foundation donated the Dannie and Hettie Heineman Collection to the library; and in 1972 Robert Owen Lehman put on deposit his stellar collection of music manuscripts. This article identifies some of the highlights of these collections, and briefly describes the library's Gilbert and Sullivan Collection, its collection of letters of musicians, and the James Fuld Collection, by all accounts the finest private collection of printed music in the world, which the library recently agreed to purchase.