1. I would like to thank the director, Dr. Julián Martín Abad, and the staff of the Manuscript Division of the Biblioteca Nacional and Sa V. Reyes Carmona of the Biblioteca de la Universidad for their generous help during my visits; the Wissenschaftliche Gesellschaft (Freiburg i. Br.) for its support with the acquisition of microfilm copies of many manuscripts, and the National Endowment for the Humanities (Washington, D.C.) for its financial assistance with the preparation of this catalogue.