The Protomedicato was born, developed, and declined in the central administration of the Castilian Kingdom during the historic period known as the Modern Age (15th-19th centuries). The main objective of this study was to produce a conceptual analysis of this royal institution, a high collegiate court of technical character whose aim was to control all health-related professions in Castile; it had an independent jurisdiction and was not subordinate to the Royal Council (Consejo Real), although it was sometimes influenced by this council. We studied the legislative and everyday life and evolution of this court through different stages in its long life span. The Protomedicato, considered not as an isolated institution but within the bureaucracy of modern administration, is analyzed in the context of its sometimes strained relationship with other national, regional and local institutions of the Kingdom, the University, the Church and the Professional Association.