Sir William Monson (born 1568, Lincolnshire, Eng.—died February 1643, Kinnersley, Surrey) was an English naval officer best-known for his Naval Tracts.

He entered Balliol College, Oxford, in 1581 but four years later ran away to sea; however, he took his degree in 1594. In the Spanish Armada campaign he served as a volunteer in the Charles pinnace and afterward accompanied George Clifford, 3rd earl of Cumberland, on three voyages to the West Indies. In 1596 he was flag captain to the earl of Essex at the capture of Cadiz, and in 1602 he was vice admiral of the last fleet to be sent against Spain, when the great carrack St. Valentine was taken. From 1604 to 1616 he was Admiral of the Narrow Seas, being chiefly engaged against pirates. He was dismissed partly for accepting bribes from Spain and partly because of his supposed connection with the murder of Sir Thomas Overbury. Monson’s last service at sea was in command of the ship-money fleet of 1635.

During his retirement he composed his Naval Tracts, which were first printed in abbreviated form in 1682, then in full in 1704, a definitive edition in five volumes being edited by M. Oppenheim for the Navy Records Society in 1902–14. It is to these writings that Monson owes his fame, since, besides being the first account by a naval officer of a war in which he himself served, they provide a valuable commentary on the Elizabethan war with Spain and conditions at sea during that period.