Lottery is a competition based on chance in which numbered tickets are sold for the chance to win a prize, typically money. Some governments outlaw lotteries, while others endorse them to some extent by organizing national or state lotteries. Regardless of their legal status, lottery games are usually characterized by the use of random numbers or symbols for determining winners and by the sharing of the prize pool among all participants.

Lotteries can be categorized by their cost and prizes, with the most expensive offering large cash prizes and the least expensive offering small amounts of cash. Prizes can also be awarded by lottery in the form of goods or services, and they may be offered as a way to raise funds for a specific cause. The first known lotteries were held in the 15th century in the Low Countries as a way to raise money for town fortifications and to help poor citizens.

The purchase of a lottery ticket can be rationalized if the entertainment value or other non-monetary benefits are sufficient to offset the disutility of a possible monetary loss. However, this can be difficult in practice, as it is generally not possible to predict the results of a lottery drawing with any accuracy. This is why many lotteries promote the message that playing the lottery is fun and harmless, and encourage people to play for the experience of buying a ticket. While this can reduce the regressivity of lottery consumption, it does not alter its essentially irreversible nature.