A game is a structured form of play undertaken for entertainment, learning, or competition. Games can be physical (such as a board game, a sport, or a video game) or virtual (such as a computer game). A game is usually played with one or more people, but may also be an activity that is observed by non-players, such as spectator sports or games. Games can be playful or serious, and may be classified as art (such as a jigsaw puzzle) or work (such as professional players of spectator sports or games). They can also be cultural icons, such as a board game that has been around for thousands of years or an e-sports tournament.

Game design is the process of creating a game. It consists of three primary stages: game concepting, game design, and game implementation. The concepting phase includes the generation of game goals and mechanics. The game designer also outlines the components of the game, including any physical objects required and any on-screen elements or characters. The mechanics and components are then tested for usability, clarity of rules, and enjoyment. If necessary, modifications are made.

The implementation phase involves bringing the game from conception to completion. This is typically done by a large development team, although small teams and independent developers can make games as well. Once the game is complete, it is ready to be released. Game publishers act as distributors and retailers, distributing the game media to consumers and selling it in stores or digital marketplaces. Retailers include department and electronic stores, specialty game stores, and online retailers. They may sell new and used games, and often offer a trade-in program for used games.

There is a significant body of game theory, which studies the principles of fair and unfair play. This is particularly evident in sports, but also extends to games of chance and chess. A game can be analyzed using mathematical methods, which are described in detail by game theorists. These methods involve identifying the players, the information and actions they have available at each decision point, the payoffs for each possible outcome, and the strategies that the players may employ to reach an equilibrium of the game.

A game is also often characterized by its tools, which are used to interact with the environment and produce changes in the state of the game. The most common tool is the game board, but other examples include pieces in a chess set, physical tokens in a tug of war, or intangible items such as play money in a casino. Some games do not use any obvious tools and instead rely on the environment to define interactivity. For example, the gameplay of hide-and-seek can vary radically depending on the room in which it is played.