William Byrd (; c. 1540 – 4 July 1623) was an English Renaissance composer. Considered among the greatest composers of the Renaissance, he had a profound influence on composers both from his native country and on the Continent. He is often considered along with John Dunstaple and Henry Purcell as one of England's most important early music composers.

Byrd wrote in many of the forms current in England at the time, including various types of sacred and secular polyphony, keyboard (the so-called Virginalist school), and consort music. He produced sacred music for Anglican services, but during the 1570s became a Roman Catholic, and wrote Catholic sacred music later in his life.