Gambling is the wagering of money or something of material value as the stakes on an event with an uncertain outcome with the primary intent of winning additional money and or material goods. Typically, the outcome of the wager is evident within a short period. Gaming refers to instances in which the law permits the type of gambling. Gaming and gambling are not mutually exclusive. A gaming company offers legal gambling activities to the public and a gaming control board may regulate the gaming company, like the Nevada Gaming Control Board. However, the English-speaking world does not acknowledge this distinction often. For instance, in the UK, the regulator of gambling activities is called the Gambling Commission not the Gaming Commission. In addition, the word gaming describes activities that do not involve wagering, especially online. Gambling is also a major international commercial activity, with the legal gambling market totaling an estimated $335 billion in 2009. Under United States federal law, gambling is legal in the country and states are free to regulate or prohibit the practice. Gambling has been legal in Nevada since 1931, forming the backbone of the economy of the state. The city of Las Vegas is perhaps the best known gambling destination in the world. In 1976, gambling became legal in Atlantic City, New Jersey and in 1990, under state law, gambling became permissible in Tunica, Mississippi; both of those cities have developed extensive casino and resort areas since then. Since a favorable United State Supreme Court decision in 1987, many American Indian tribes have built their own casinos on tribal lands as a way to provide revenue for the tribe. Because the tribes are sovereign nations, they are often exempt from state laws that restrict gambling and are instead regulated under federal law.

Betting arbitrage, miracle bets, sure bets, sports arbitraging is a particular case of arbitrage arising on betting markets due to bookmakers’ different opinions on either event outcomes or plain errors. By placing one bet per each outcome with different betting companies, the bettor can make a profit. In the bettors' slang an arbitrage is often referred to as an arb; people who use arbitrage are called arbers. A typical arb is around 2 percent, often less; however 4-5 percent are occasionally seen and during some special events they might reach 20 percent. Arbitrage betting involves relatively large sums of money stakes are bigger than in normal betting.

Bookmakers generally disapprove of arbers, and restrict or close the accounts of those who they suspect of engaging in arbitrage betting. Although arbitrage betting has existed since the beginnings of bookmaking, the rise of the Internet, odds-comparison websites and betting exchanges have enabled the practice to be easier to perform. On the other hand, these changes also made it easier for bookmakers to keep their odds in line with the market.

The best way of generating profit, which has been established in Britain via sports arbitrage, consists of 'key men' employing others to place bets on their behalf, so as to avoid detection and increase accessibility to bookmakers. This allows the financiers or key arbers to stay at a computer to keep track of market movement.

While often claimed to be risk-free, this is only true if an arb is successfully completed; in reality, there are several threats to this:

Arbs in online sports markets have a median lifetime of around 15 minutes, after which the difference in odds underpinning them vanishes through betting activity. Without rapid alerting and action, it is possible to fail to make all the legs of the arb before it vanish, thus transforming it from a risk-free arb into a bet. High street bookmakers however, offer their odds days in advance and rarely change them once they have been set. These Arbs can have a lifetime of several hours.

Making errors: In the excitement of the action and due to the high number of bets placed, it is not uncommon to make a mistake like traders on financial markets. For example the appropriate stakes may be incorrectly calculated, or be placed on the wrong legs of the arb, locking in a loss, or there may be inadequate funds in one of the accounts to complete the arb. Those errors might temporarily have an important impact. In the long term, the benefit will depend on the odds. For example one could actually make more money by placing the wrong bet where the outcome happens to be beneficial, though not justified by the arbitrage calculation. However, this stroke of luck being repeated is unlikely, assuming the bookies have calculated the odds so they make a profit.

Bet cancellation: If a bettor places bets so as to make an arbitrage and one bookmaker cancels a bet, the bettor could find himself in a bad position because he is actually betting with all the risks implied. The bettor can repeat the bet that has been cancelled so as minimize the risk, but if he cannot get the same odds he had before he may be forced to take a loss. In some cases the situation arises when there are very high potential payouts by the bookie, perhaps due to an unintentional error made while quoting odds. Many jurisdictions allow bookmakers to cancel bets in the event of such a palpable [obvious] error in the quoted odds This is often loosely defined as an obvious mistake, but whether a palp in fact has been made is often the sole discretion of the bookmaker.

Other problems: Bookmakers who suspect arbing can set very low maximum stake limits, making arbing insufficiently profitable. Capital diffusion is serious; many bookmakers make it very easy to deposit funds and difficult to withdraw them. Making a return involves many bets spread over typically many bookmakers so keeping track is a considerable challenge, and requires excellent record-keeping.