The House of Aviz (Portuguese: Casa de Avis [ɐˈviʃ]), also known as the Joanine Dynasty (Dinastia Joanina), was a dynasty of Portuguese origin which flourished during the Renaissance and the period of the Portuguese discoveries, when Portugal expanded its power globally.

The house was founded by King John I of Portugal, Grand-Master of the Order of Aviz and illegitimate son of King Pedro I (of the Portuguese House of Burgundy), who ascended to the throne after successfully pressing his claim during the 1383–1385 Portuguese interregnum. Aviz monarchs would rule Portugal through the Age of Discovery, establishing Portugal as a global power following the creation of the Portuguese Empire. In 1494, Pope Alexander VI divided the world under the dominion of Portugal and Spain with the Treaty of Tordesillas.

The House of Aviz has produced numerous prominent figures in both European and global history, including Prince Henry the Navigator, King Manuel I of Portugal, and Holy Roman Empress Isabella of Portugal. Numerous Aviz dynasts have also claimed thrones or titles across Europe, including King Peter V of Aragon and John, Prince of Antioch. The Aviz ruled Portugal from 1385 until 1580, when the Philippine Dynasty succeeded to the throne following the Portuguese succession crisis of 1580.

The founder of the House of Aviz, King John I of Portugal, was born in 1357 as the illegitimate child of King Pedro I of Portugal, a member of the Portuguese House of Burgundy, and Teresa Lourenço, daughter of a Lisbon merchant. In 1364, at 7 years old, John was made Grand Master of the Order of Aviz, henceforth becoming known as John of Aviz.

The House of Aviz was established as a result of the dynastic crisis following the 1383 death of Ferdinand I. Ferdinand's widow Leonor Telles was disliked by both the nobility and the commoners for having left her first husband and for having had their marriage annulled in order to marry King Ferdinand. Ferdinand's designated heir was their only surviving child Beatrice, married to John I of Castile who claimed the throne in the name of his wife, but under the Treaty of Salvaterra that had been the basis for John's marriage to Beatrice, the unpopular Leonor was left as Regent until such time as the son of Beatrice and John would be 14 years old.

In April 1385, amidst popular revolt and civil war, the Cortes of Coimbra declared John, Master of Aviz, as king John I of Portugal. He was half-brother of Ferdinand and natural son of Ferdinand's father and predecessor Pedro I. He had the particular backing of the rising bourgeoisie of Lisbon; the nobility were split, with the majority favoring the legitimist Beatrice. Troops under General Nuno Álvares Pereira defeated a small Castilian army at Atoleiros, while John of Castile had to lift a siege to Lisboa, mainly due to a plague that hit his army and killed his wife Beatrice. This was followed, however, by a larger invasion of Castilian and Portuguese troops loyal to John of Castile.

John of Aviz's rule became established fact with the Portuguese victory in the Battle of Aljubarrota on 14 August 1385, where he defeated John I of Castile. A formal peace between Portugal and Castile would not be signed until 1411.

To mark his victory, John founded the Monastery of Santa Maria da Vitória, known as the "Batalha Monastery" ("Battle Monastery"), whose chapel became the burial place of the princes of the new dynasty of Aviz. The descendants of King John I were still also Masters of Aviz, though at times that title passed to one descendant of John and the Crown of Portugal to another. The title of Grand Master of the Order of Aviz was permanently incorporated into the Portuguese Crown toward the end of rule by the House of Aviz, in 1551.