Swiss mercenaries (Reisläufer) were notable for their service in foreign armies, especially the armies of the Kings of France, throughout the Early Modern period of European history, from the Later Middle Ages into the Age of the European Enlightenment. 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 Swiss Guard at the Vatican.
In William Shakespeare's Hamlet, Act IV, Scene 5, Swiss mercenaries are called "Switzers" (Switzer is actually what the Swiss were called in English until the 19th century).