A lottery is an arrangement in which one or more prizes are allocated by a process that relies wholly on chance. It may involve a single winner or it may have several winners, depending on the type of lottery and the specifics of its rules.

The lottery has long been a popular form of gambling, and it is sometimes used to raise money for various public uses. In the early 15th century, local towns in the Low Countries held public lotteries to raise money for town fortifications and for poor relief. The modern concept of a lottery is usually associated with a prize money pool from which the winners are selected at random. The prizes may be monetary, or they can take the form of goods or services.

There are some basic requirements that all lotteries must meet. First, a system must be in place for collecting and pooling all the money that people pay as stakes. This is often done by passing the money paid for tickets up a hierarchy of sales agents until it reaches a central organization. A computer system is also often used for storing information about the tickets and generating winning numbers.

Another important requirement is that a procedure must be in place for selecting the winners. Usually this involves thoroughly mixing the tickets or their counterfoils by some mechanical means (such as shaking or tossing) before extracting the winners from them. A computer is increasingly being used to do this because of its ability to store and manage large numbers of tickets and generate the winning numbers.