The successful shipmaster or magister of a medieval ship possessed many skills: navigational expertise to guide the vessel to its destination; commercial acumen to dispose of cargoes in his charge; management ability to employ, victual and direct a crew of men who were often of disparate backgrounds and ethnicities; business savvy to cope with wily seamen, shore-side workers and merchants in foreign ports; initiative to handle the dangers and risks that pervaded life at sea; and a basic understanding of law and international politics to steer his ship, cargo and crew through the dangerous waters of the medieval seas. This essay focuses on the entrepreneurial skills that medieval English shipmasters needed to be successful, particularly in terms of shipowning, naval service, remuneration, trade, managerial skills and the hazy border between privateering and piracy. Shipmasters often had an important stake in individual trading voyages, particularly when they owned all or part of the ship or had some share of the cargo. Even when their ownership stake was small, their ability to react quickly to ever-changing circumstances — whether a shift in the wind that kept them in a foreign port for weeks on end, or the loss of cargo in a storm, attacks by pirates, a shortage of the goods customers wanted or the loss of crewmen to illness or death — was essential since they were most responsible for the ultimate profit or loss of the voyage.