Johannes Ockeghem (c. 1410 – 6 February 1497) was a Franco-Flemish composer and singer of early Renaissance music. Ockeghem was a significant European composer in the period between Guillaume Du Fay and Josquin des Prez, and he was—with his colleague Antoine Busnois—a prominent European composer in the second half of the 15th century. He was an important proponent of the early Franco-Flemish School.

Ockeghem was well associated with other prominent composers of the time, and spent most of his career serving the French royal court under Charles VII, Louis XI and Charles VIII. Numerous poets and musicians lamented his death, including Erasmus, Guillaume Crétin, Jean Molinet and Josquin, who composed the well-known Nymphes des bois for him.

It is thought that Ockeghem's extant works represent only a small part of his entire oeuvre, including around 14 masses, 20 chansons and fewer than 10 motets—though the exact numbers vary due to attribution uncertainties. His better-known works include the canon-based Missa prolationum; the Missa cuiusvis toni, which can be sung in any mode; the chanson Fors seulement; and the earliest surviving polyphonic Requiem.

The spelling of Ockeghem's name comes from a supposed autograph of his which survived as late as 1885, and was reproduced by Eugène Giraudet, a historian in Tours; the document has since been lost. In 15th-century sources, the spelling "Okeghem" predominates. Other spellings include Ogkegum, Okchem, Hocquegam and Ockegham.

Ockeghem is believed to have been born in the Walloon city Saint-Ghislain, Burgundian Netherlands (now Belgium). His birthdate is unknown; dates as early as 1410 and as late as 1430 have been proposed. The earlier date is based on the possibility that he knew Binchois in Hainaut before the older composer moved from Mons to Lille in 1423. Ockeghem would have to have been younger than 15 at the time. This particular speculation derives from Ockeghem's reference, in the lament he wrote on the death of Binchois in 1460, to a chanson by Binchois dated to that time. In this lament, Ockeghem not only honored the older composer by imitating his style, but also revealed some useful biographical information about him. The comment by the poet Guillaume Crétin, in the lament he wrote on Ockeghem's death in 1497, "it was a great shame that a composer of his talents should die before 100 years old", is also often taken as evidence for the earlier birthdate for Ockeghem.

In 1993, documents dating from 1607 were found stating that "Jan Hocquegam" was a native of Saint-Ghislain in the County of Hainaut, which was confirmed by references in 16th-century documents. This suggests that, though he first appears in records in Flanders, he was a native speaker of Picard. Previously, most biographies surmised that he was born in East Flanders, either in the town after which he was named (present-day Okegem, from which his ancestors must have come) or in the neighboring town of Dendermonde (French: Termonde), where the surname Ockeghem occurred in the 14th and 15th century. Occasionally, Bavay, now in the Nord department in France, was suggested as his birthplace as well.

Details of his early life are lacking. Like many composers in this period, he started his musical career as a chorister, although the exact location of his education is unknown: Mons, a town near Saint-Ghislain that had at least two churches with competent music schools, has been suggested. The first actual documented record of Ockeghem is from the Onze-Lieve-Vrouwe cathedral in Antwerp, where he was employed in June 1443 as a "left-hand choir singer" ("left-handers" sang composed music, "right-handers" sang chant). He probably sang under the direction of Johannes Pullois, whose employment also dates from that year. This church was a distinguished establishment, and it was likely here that Ockeghem became familiar with the English compositional style, which some suggest influenced musical practices on the continent in the late 15th century.

Ockeghem probably studied with Gilles Binchois, and at least was closely associated with him at the Burgundian court. Since Antoine Busnois wrote a motet in honor of Ockeghem sometime before 1467, it is probable that those two were acquainted as well; and writers of the time often link Dufay, Busnois and Ockeghem. Although Ockeghem's musical style differs considerably from that of the older generation, it is probable that he acquired his basic technique from them, and as such can be seen as a direct link from the Burgundian style to the next generation of Netherlanders, such as Obrecht and Josquin.