Although many animals play, only humans confirmably have games. Whether some animals are intelligent enough to game is debatable, though a game has ritualistic elements (such as rules and procedures) that are voluntarily acted upon, rather than as a result of instinct. The existence of rules and criteria that decide the outcome of games imply that games require intelligence of a significant degree of sophistication.

Non-human animal species may, however, engage in games whose rules and sophistication may be of such a nature as to be incapable of detection by humans in their present state of knowledge. It would, for example, seem incongruous that large brained species such as many Cetaceans and the larger hominids did not play games. Our inability to observe and understand such games should not be taken as a confirmation that they do not exist. Some courtship displays by some species of bird, such as the Black Grouse, appear to have a component which, from an anthropolgical view, might appear to be a game in which there are clearly winners and losers.

Games can involve one player acting alone, or two or more players acting cooperatively. Most often involve competition among two or more players. Taking an action that falls outside the rules generally constitutes a foul or cheating.

All through human history, people have played games to entertain themselves and others. There are an enormous variety of games; for specific information about different types of games, see the links at the end of this article.

Philosopher David Kelley, in his popular introductory reasoning text The Art of Reasoning, defines the concept "game" as "a form of recreation constituted by a set of rules that specify an object to be attained and the permissible means of attaining it." This covers most cases well, but does not quite fit with things like war games and sports , which often are not played for entertainment but to build skills for later use.

The recent popularity of video game studies has lead to renewed interest in game definitions.

Games in philosophy

In Philosophical Investigations, philosopher Ludwig Wittgenstein argued that the concept "game" could not be contained by any single definition, but that games must be looked at as a series of definitions that share a "family resemblance" to one another. Games were important to Wittgenstein's later thought; he held that language was itself a game, consisting of tokens governed by mutually agreed upon rules that governed the usage of words.

Stanley Fish, looking for a clear example of the sorts of social constructions, cited the balls and strikes of baseball as example. While the strike zone target is governed by the rules of the game, it epitomizes the category of things that exist only because people have agreed to treat them as real. No pitch is a ball or a strike until it has been labelled as such by an appropriate authority, the plate umpire, whose judgment on this matter cannot be challenged within the current game.

Many technical fields are often applied to the study of games, including probability, statistics, economics, ethnomathematics, and game theory.

Anthropology of games

Games, being a characteristic human activity strongly determined by custom and the frequent subjects of folklore, have been the subject of anthropological investigations.

Classes of games

While many different subdivisions have been proposed, anthropologists classify games under three major headings, and have drawn some conclusions as to the social bases that each sort of game requires. They divide games broadly into:

• Games of pure skill, such as hopscotch and target shooting;
• Games of pure strategy, such as checkers, go, or tic-tac-toe;
• Games of chance, such as craps and snakes and ladders.

In addition to these basic classifications, there are mixed games; such as football, partly a game of skill and partly a game of strategy; poker, partly a game of strategy and partly a game of chance; and baseball, which combines elements of all three. Baseball Hall of Famer Casey Stengel underscored this point when he remarked, "I had many years when I was not so successful as a ballplayer, as it is a game of skill."