During the late Middle Ages, mercenary forces grew in importance in Europe, as veterans from the Hundred Years' War preferred to continue living a soldier's life rather than abandoning the military. Swiss mercenaries (Reisläufer) in particular were valued for their loyalty and skills, and several European countries—mainly the Netherlands and France—had Swiss Pikemen regiments in their armed forces under treaties with the various Swiss cantons.

The native term Reisläufer literally means "one who goes to war" and is derived from Middle High German Reise meaning "military campaign".

Since 1859 however, only one mercenary unit is permitted under Swiss law, certainly the most famous of all: the Vatican's Swiss Guard, which has been protecting the Pope for the last five centuries.