A lottery is a form of gambling which involves the drawing of lots for a prize. Some governments outlaw it, while others endorse it to the extent of organizing a national lottery. It is common to find some degree of regulation of lottery by governments.

At the beginning of the 20th century, most forms of gambling, including lotteries and sweepstakes, were illegal in many countries, including the U.S.A. and most of Europe. This remained so until after World War II. In the 1960s casinos and lotteries began to appear throughout the world as a means to raise revenue in addition to taxes.
National Lottery building located on Paseo de la Reforma in Mexico City.

Lotteries are most often run by governments or local states and are sometimes described as a regressive tax, since those most likely to buy tickets will typically be the less affluent members of a society. The astronomically high odds against winning the larger prizes have also led to the epithets of a "tax on stupidity" or "math tax". Although the use of the word "tax" is not strictly correct, these descriptions are intended to suggest that lotteries are government-sanctioned operations which will attract only those people who fail to understand that buying a lottery ticket is a poor economic decision. Indeed, after taking into account the present value of a given lottery prize as a single lump sum cash payment, the impact of any taxes that might apply, and the likelihood of having to share the prize with other winners, it is not uncommon to find that a ticket for a typical major lottery is worth less than one third of its purchase price. In other words, if a lottery ticket costs US$1 to purchase, its true economic worth may be only US$0.30 or so at the time of purchase. Of course, this is just a hypothetical example and the actual calculation will be dependent upon the specific details of each lottery. Some lotteries may offer tickets that are worth less than 20% of their price, while others may be worth over 50%. The underlying point is that in order to raise money, lottery operators must ensure that tickets are worth substantially less than what they cost to buy, thereby making the lottery a bad deal for its customers.