This book examines Santiago Kastner’s paramount role in applying musicology to performance from the 1930s to the 1980s. His European tours as keyboard player heralded his commitment to the spreading of early Iberian music, then secured by appointments in Portuguese and Spanish institutions. Three case studies, focused on Seixas, Soler and Cabezón, delve into his approach to the repertoire by means of its study, edition and interpretation and into his impact in creating a performing tradition.