Willaert, Adrian, c.1490-1562, Flemish composer. After brief engagements at Ferrara and Milan, he was choirmaster at St. Mark's, Venice, from 1527 until his death. Willaert was the founder of the Venetian school of composition. His polychoral settings of psalms and the Magnificat helped popularize this technique, and he and his followers were important in the development of the madrigal. Among his works are masses, motets, instrumental ricercari, and French and Italian secular songs.