A jester, court jester, fool or joker was a member of the household of a nobleman or a monarch employed to entertain guests during the medieval and Renaissance eras. Jesters were also itinerant performers who entertained common folk at fairs and town markets, and the discipline continues into the modern day, where jesters perform at historical-themed events.

During the Middle Ages, jesters are often thought to have worn brightly colored clothes and eccentric hats in a motley pattern. Their modern counterparts usually mimic this costume. Jesters entertained with a wide variety of skills: principal among them were song, music, and storytelling, but many also employed acrobatics, juggling, telling jokes (such as puns, stereotypes, and imitation), and performing magic tricks. Much of the entertainment was performed in a comic style. Many jesters made contemporary jokes in word or song about people or events well known to their audiences.