Alvaro de Luna was for almost forty years Juan II of Castile's closest friend, and for the greater part of that time his chief minister. Working ceaselessly to consolidate Juan's position, achieved through his great-grandfather's murder of his half-brother king Pedro, he had initially to establish a power base and, in the years preceding his eventual downfall, to maintain it against the constant restlessness of the Spanish nobility. Only in the middle years can he be seen to have given Spain a fiscal regime, an enterprising recruitment policy for the public services, and a coherent ideology. This study of the violent and enigmatic circumstances in which his career came to an end makes a valuable contribution to understanding 15th-century Castilian history.