One of Europe's great queens, Isabella of Castile is also one of the least well known, but undeservedly so. For no other European queen in history can fully rival her power or achievements as a female ruler who overcame huge obstacles. Formidable, tenacious and ambitious, as a teenager she saw off rivals to the crown from within her own family before going on to rule Castile in her own right. Isabella was only twenty-three years old in 1474 when she ascended the throne of Castile, the largest and strongest kingdom in Hispania. At a time when successful queens were few and far between, Isabella faced not only the considerable challenge of being a young, female ruler in an overwhelmingly male-dominated world, but also of reforming a major European kingdom riddled with crime, debt, corruption and religious factionism. Her marriage to Ferdinand of Aragon united two kingdoms, a royal partnership in which Isabella more than held her own. Her pivotal reign was long and transformative, leaving behind a legacy that would resonate across the centuries that followed. By the time of her death in 1504, Isabella had laid the foundations not just of modern Spain, but of one of Europe's greatest empires. In this biography, Tremlett chronicles the life of Isabella of Castile as she led her country out of the middle ages and harnessed the newest ideas and tools of the early Renaissance to turn her ill-disciplined nation into a truly modern state with a powerful and ambitious monarch at its centre. With authority and insight, he relates the story of one of the most legendary and controversial of great European queens.