The Catholic monarchs (Spanish: Reyes Católicos) is the collective title used in history for Queen Isabella I of Castile and King Ferdinand II of Aragon. They married in 1469, uniting both crowns and eventually through their decendants creating the kingdom of Spain. The title "Catholic King" was bestowed on them by Pope Alexander VI.

Although the Queen had several Converso counselors, the monarchs' Catholic views led them to end the independence of Moors in the Iberian Peninsula with the conquest of Granada and to force the expulsion or conversion of thousands of Sephardic Jews (see Alhambra Decree). The Spanish Inquisition, inspired by earlier European Inquisitions, was created by their royal decree.

Their joint motto was Tanto monta, monta tanto ("It amounts so, so it amounts").

It was created by Antonio de Nebrija and was either:

• an allusion to the Gordian Knot: Tanto monta, monta tanto, cortar como desatar ("..., cutting as untying")
• explaining the equal footing for both monarchs in the governance of Castile: Tanto monta, monta tanto, Isabel como Fernando ("..., Isabella as Ferdinand")

Their symbol was el yugo y las flechas, a yoke and a fasces of arrows. The yoke is another allusion to the Gordian knot. Y and F are the initials of Ysabel (archaic spelling) and Fernando. This symbol was later used by the Spanish fascist party the Falange, which claimed the glory and the ideals of the Reyes Católicos.