The Treaty of Villafáfila is a treaty signed by Ferdinand the Catholic in Villafáfila on 27 June 1506 and by Philip the Handsome in Benavente, Zamora, on 28 June.
The treaty recognised the incapacity of Ferdinand's daughter and Philip's wife, Joanna the Mad, to reign on her own as Queen of Castile. Joanna had succeeded her mother, Isabella the Catholic, who had appointed her husband and co-ruler Ferdinand as regent of Castile in the name of their mentally unstable daughter. However, Joanna's husband Philip demanded his share in the government. The Treaty of Villafáfila followed the Treaty of Salamanca, in which Ferdinand and Philip were recognised as co-regents in Joanna's name. However, the new treaty required Ferdinand to cede all power to Philip and retire to his own hereditary realms, the Crown of Aragon, to which Joanna was also heir presumptive, and proclaimed Philip King of Castile jure uxoris.
The treaty lost all meaning soon after it was signed, as King Philip I died on 25 September, leaving Ferdinand free to return to Castile and again assume regency, which he held until his death.