The Swiss mercenaries were a powerful infantry force constituted by professional soldiers originating from the cantons of the Old Swiss Confederacy. They were notable for their service in foreign armies, especially among the military forces of the kings of France, throughout the early modern period of European history, from the Late Middle Ages into the Renaissance. Their service as mercenaries was at its peak during the Renaissance, when their proven battlefield capabilities made them sought-after mercenary troops. There followed a period of decline, as technological and organizational advances counteracted the Swiss' advantages. Switzerland's military isolationism largely put an end to organized mercenary activity; the principal remnant of the practice is the Pontifical Swiss Guard at the Vatican.

The Old Swiss Confederacy, also known as Switzerland or the Swiss Confederacy, was a loose confederation of independent small states, initially within the Holy Roman Empire. It is the precursor of the modern state of Switzerland.