Adrian Willaert (c. 1490–December 7, 1562) was a Flemish composer of the Renaissance and founder of the Venetian School. He was one of the most representative members of the generation of northern composers who moved to Italy and transplanted the polyphonic Franco-Flemish style there.

Life
He was probably born at Bruges, although a secondary source has suggested Roulers. According to his student, the renowned late 16th century music theorist Gioseffo Zarlino, Willaert went to Paris first to study law, but instead decided to study music. In Paris he met Jean Mouton, the principal composer of the French royal chapel and stylistic compatriot of Josquin Desprez, and studied with him.
Sometime around 1515 Willaert first went to Rome. An anecdote survives which indicates the musical ability of the young composer: Willaert was surprised to discover the choir of the papal chapel singing one of his own compositions, most likely the six-part motet Verbum vonum et suave, and even more surprised to learn that they thought it had been written by the much more famous composer Josquin. When he informed the singers of their error—that he was in fact the composer—they refused to sing it again. Indeed Willaert's early style is very similar to that of Josquin, with smooth polyphony, balanced voices and frequent use of imitation.
In July 1515, Willaert entered the service of Cardinal Ippolito I d'Este of Ferrara. Ippolito was a traveler, and Willaert likely accompanied him to various places, including Hungary, where he likely resided from 1517 to 1519. When Ippolito died in 1520, Willaert entered the service of duke Alfonso of Ferrara. In 1522 Willaert had a post at the court chapel of Duke Alfonso; he remained there until 1525, at which time records show he was in the employ of Ippolito II d'Este in Milan.
Willaert's most significant appointment, and one of the most significant in the musical history of the Renaissance, was his selection as maestro di cappella of St. Mark's at Venice. Music had languished there under his predecessor, Pietro de Fossis, but that was shortly to change.
From his appointment in 1527 until his death in 1562, he retained the post at St. Mark's. Composers came from all over Europe to study with him, and his standards were high both for singing and composition. During his previous employment with the dukes of Ferrara, he had acquired numerous contacts and influential friends elsewhere in Europe, including the Sforza family in Milan; doubtless this assisted in the spread of his reputation, and the consequent importation of musicians from foreign countries into northern Italy.

Musical style and influence
Willaert was one of the most versatile composers of the Renaissance, writing music in almost every extant style and form. In force of personality, and with his central position as maestro di cappella at St. Mark's, he became the most influential musician in Europe between the death of Josquin and the time of Palestrina.
According to Gioseffo Zarlino, writing later in the 16th century, Willaert was the inventor of the antiphonal style from which the polychoral style of the Venetian school evolved. As there were two choir lofts, one of each side of the main altar of St. Mark's, both provided with an organ, Willaert divided the choral body into two sections, using them either antiphonally or simultaneously. He then composed and performed psalms and other works for two alternating choirs. This innovation met with instantaneous success and strongly influenced the development of the new method. In 1550 he published Salmi spezzati, antiphonal settings of the psalms, the first polychoral work of the Venetian school. While more recent research has shown that Willaert was not the first to use this antiphonal, or polychoral method — Dominique Phinot had employed it before Willaert, and Johannes Martini even used it in the late 15th century — Willaert's polychoral settings were the first to become famous and widely imitated.
Willaert was no less distinguished as a teacher than as a composer. Among his disciples are: Cipriano de Rore, his successor at St. Mark's; Costanzo Porta; Francesco Dalla Viola; Gioseffo Zarlino; and the two Gabrielis, Andrea and Giovanni. These formed the core of what came to be known as the Venetian school, which was decisively influential on the stylistic change which marked the beginning of the Baroque era. Willaert left a large number of compositions - 8 masses, over 50 hymns and psalms, over 150 motets, about 60 French chansons, over 70 Italian madrigals and several instrumental (ricercares).