Gambling (also known as betting or gaming) is the wagering of something of value ("the stakes") on a random event with the intent of winning something else of value, where instances of strategy are discounted. Gambling thus requires three elements to be present: consideration (an amount wagered), risk (chance), and a prize. The outcome of the wager is often immediate, such as a single roll of dice, a spin of a roulette wheel, or a horse crossing the finish line, but longer time frames are also common, allowing wagers on the outcome of a future sports contest or even an entire sports season.

The term "gaming" in this context typically refers to instances in which the activity has been specifically permitted by law. The two words are not mutually exclusive; i.e., a "gaming" company offers (legal) "gambling" activities to the public and may be regulated by one of many gaming control boards, for example, the Nevada Gaming Control Board. However, this distinction is not universally observed in the English-speaking world. For instance, in the United Kingdom, the regulator of gambling activities is called the Gambling Commission (not the Gaming Commission). The word gaming is used more frequently since the rise of computer and video games to describe activities that do not necessarily involve wagering, especially online gaming, with the new usage still not having displaced the old usage as the primary definition in common dictionaries. "Gaming" has also been used euphemistically to circumvent laws against "gambling". The media and others have used one term or the other to frame conversations around the subjects, resulting in a shift of perceptions among their audiences.

Gambling is also a major international commercial activity, with the legal gambling market totaling an estimated $335 billion in 2009. In other forms, gambling can be conducted with materials that have a value, but are not real money. For example, players of marbles games might wager marbles, and likewise games of Pogs or Magic: The Gathering can be played with the collectible game pieces (respectively, small discs and trading cards) as stakes, resulting in a metagame regarding the value of a player's collection of pieces.

Gambling dates back at least to the Paleolithic period, before written history. In Mesopotamia the earliest six-sided dice date to about 3000 BCE. However, they were based on astragali dating back thousands of years earlier. In China, gambling houses were widespread in the first millennium BCE, and betting on fighting animals was common. Lotto games and dominoes (precursors of Pai Gow) appeared in China as early as the 10th century.

Playing cards appeared in the 9th century CE in China. Records trace gambling in Japan back at least as far as the 14th century.

Poker, the most popular U.S. card game associated with gambling, derives from the Persian game As-Nas, dating back to the 17th century.

The first known casino, the Ridotto, started operating in 1638 in Venice, Italy.

Gambling has been a main recreational activity in Great Britain for centuries. Queen Elizabeth I chartered a lottery that was drawn in 1569. Horseracing has been a favorite theme for over three centuries. It has been heavily regulated. Historically much of the opposition comes from Nonconformist Protestants, and from social reformers.