This is a comprehensive study in English of political thought in Spain during the Renaissance. In the early sixteenth century Castile experienced two major constitutional crises caused by the accession of a Habsburg ruler (shortly to become Holy Roman Emperor) to her throne, and by the discovery and conquest of America. Politically, these circumstances created a bizarre situation in which the venerable idea of medieval empire was forced to co-exist with a novel, imperial vision made inevitable by expansion in the new world. The strain imposed on Castile's constitutional fabric stimulated the most significant developments of Spanish political thought in the Renaissance. Against this background, Professor Fernández-Santamaria surverys the contribution of a number of eminent writers from diverse intellectual traditions who endeavoured to apply established political assumptions to these unprecedented circumstances.