The lottery is a game of chance in which participants purchase tickets for a chance to win a prize. Prizes may be money or goods or services. Lotteries are regulated by governments or private organizations and operate under laws governing their operation, promotion and prizes. In the United States, 44 states and the District of Columbia have lotteries. In addition, a number of countries offer national and regional lotteries.

The first known lotteries were held in the Low Countries in the 15th century to raise funds for town fortifications and the poor. In colonial America, the games became an important source of financing for public works projects including paving streets and building wharves. George Washington even sponsored a lottery to fund a road across the Blue Ridge Mountains.

A key element of any lottery is the drawing, a procedure for selecting winners by random selection from a pool of tickets or counterfoils. The pool is thoroughly mixed by some mechanical means, often shaking or tossing, and then the winning numbers or symbols are extracted. Computers are increasingly used in this process, as they can store information about large numbers of tickets and have the capacity to generate random numbers for each draw.

A rational population would correctly calculate the expected value of a ticket and reduce their willingness to participate in a lottery with a lower than average return. But researchers and IRB members who choose to use a lottery instead of a straight payment are trading on that irrationality, knowing that the participants will not rationally minimize their participation.