The War of the Castilian Succession was the military conflict contested from 1475 to 1479 for the succession of the Crown of Castile fought between the supporters of Joanna 'la Beltraneja', reputed daughter of the late monarch Henry IV of Castile, and those of Henry's half-sister, Isabella, who was ultimately successful.

The Crown of Castile was a medieval polity in the Iberian Peninsula that formed in 1230 as a result of the third and definitive union of the crowns and, some decades later, the parliaments of the kingdoms of Castile and León upon the accession of the then Castilian king, Ferdinand III, to the vacant Leonese throne. It continued to exist as a separate entity after the personal union in 1469 of the crowns of Castile and Aragon with the marriage of the Catholic Monarchs up to the promulgation of the Nueva Planta decrees by Philip V in 1715.