A ball, a racket, and a net. The simplicity of tennis is one reason that its origins are difficult to pinpoint. At any one point in time, variations of the game were probably played in almost every country in the world. Some historians believe the game was first invented in the Middle Ages—it is mentioned in twelfth-century manuscripts—but exactly when and where is probably lost to antiquity. The word tennis is derived from the French word "tenez," meaning "to hold." Certainly the French greatly enjoyed the game, and by the sixteenth century up to 2,000 Jeu-de-Paume (the name for the ball) courts had been built in France, and it is thought that every western European country had courts at the time.

Perhaps until the nineteenth century, tennis courts were walled, and the exact rules of the game may have differed from country to country, perhaps even court...