This work is the winner of the 2007 AMS Robert M. Stevenson prize. The arrival of Francisco de Penalosa at the Aragonese court in May 1498 marks something of an epoch in the history of Spanish music: Penalosa wrote in a mature, northern-oriented style, and his sacred music influenced Iberian composers for generations after his death. Kenneth Kreitner looks at the church music sung by Spaniards in the decades before Penalosa, a repertory that has long been ignored because much of it is anonymous and because it is scattered through manuscripts better known for something else.He identifies sixty-seven pieces of surviving Latin sacred music that were written in Spain between 1400 and the early 1500s, and he discusses them source by source, revealing the rapid and dramatic change, not only in the style and sophistication of these pieces, but in the level of composedly self-consciousness shown in the manuscripts. Within a generation or so at the end of the fifteenth century, Spanish musicians created a new national music just as Ferdinand and Isabella were creating a new nation. Kenneth Kreitner teaches at the University of Memphis.