John IV of Portugal (Portuguese João IV) (March 1603 - November 6, 1656), the Restoring King (Port. o Restaurador), was the 21st (or 22nd according to some historians) King of Portugal (1640 - 1656).

He was born at Vila Viçosa and succeeded his father, Teodósio II as Duke of Braganza in 1630. John married Luisa de Guzman (1613-1666), eldest daughter of the Duke of Medina-Sidonia, in 1633. By the unanimous voice of the people he was raised to the throne of Portugal (of which he was held to be the legitimate heir) during the revolution effected on December 1, 1640 against the Spanish king, Philip IV.

His accession led to a protracted war with Spain, which only ended with the recognition of Portuguese independence in a subsequent reign (1668). Portugal signed alliances with France (June 1, 1641) and Sweden (Aug 1641) but by necessity its only contribution in the Thirty Years' War were in the field against Spain and against Dutch encroachments on the Portuguese colonial empire.

In Iberia, a Spanish invasion was defeated at Montijo (1650). Abroad, the Dutch took Malacca (Jan 1641) and the Sultan of Oman captured Muscat (1648). However by 1654 most of Brazil was back in Portuguese hands and had effectively ceased to be a viable Dutch colony. This was countered by the loss of Ceilan (Portuguese Ceilão), present day Sri Lanka, to the Dutch who took Colombo in 1656.

King John IV died in 1656 and was succeeded by his son Afonso VI. His daughter Catarina married King Charles II of England.

John was a patron of music and the arts, and a considerably sophisticated writer on music; in addition to this, he was a composer. During his reign he collected one of the largest libraries in the world, but it was destroyed in the Lisbon earthquake of 1755. Among his writings is a defense of Palestrina, and a Defense of Modern Music (Lisbon, 1649).