The first dated printed book containing music was the Missale Romanum, edited by the Franciscans of the Basilica Sanctae Mariae de Ara coeli in Rome. It was printed in Rome by Ulrich Han (Udalricus Gallus), and issued on October 12, 1476, with sixteen leaves of Roman plainchant (plainsong) printed in Roman notation.
"In order to print music from movable type, music printers had to resolve two fundamental problems. First, an unvarying set of lines had to be printed for the staff, and second, music notes and signs had to be cast in metal type so that they could be printed on any line or space of that staff. These problems were resolved in both the ca. 1473 Graduale and the Han Missale of 1476 by a two-impression process. A staff of horizontal lines was printed in a first impression from what were most likely printer's rules cast in metal; next, the musical designs of plainchant, cast in type so that they could be accurately printed at any position on the staff, were printed in a separate impression. No other technical problems involved in printing music, such as the use of red and black ink for liturgical music, or the use of mensural notation rather than plainchant notation, or the use of giant-size type for choirbook format, are comparable to the fundamental difficulties mentioned above. The technique of printing staves and notes was perfected by the very first printers. Later printers of music cannot claim to have discovered or invented the basic technique but merely to have bettered it" (Duggan, Italian Music Incunabula. Printers and Type  13-14).
King, Four Hundred Years of Music Printing (1968) 10.
(This entry was last revised on 01-29-2015.)