Gambling is an activity where an individual wagers something of value, typically money, on the outcome of a contest of chance or on a future contingent event not under the control or influence of the gambler (e.g., sports events, horse races). It is distinguished from bona fide business transactions valid under the law of contracts, such as securities and commodities exchanges, insurance contracts, and guaranty and life, health, and accident insurance policies. Some forms of gambling do not involve cash; for example, players in games such as marbles, Pogs, or Magic: The Gathering may wager game pieces instead of real money.

Although the vast majority of people who gamble can stop at a few rounds of poker or a spin on a slot machine, some people become addicted to gambling. The reason for this is not simple; in addition to genetics and other psychological factors, there are some brain changes that occur with repeated gambling, which alter how chemical messages are transmitted in the prefrontal cortex, resulting in less activation of the area and an impaired ability to control impulses. Moreover, many of the same impulsive personality traits that are associated with addiction to gambling (i.e., sensation- and novelty-seeking) are also correlated with a lack of behavioral inhibition.

In psychiatry, there is no agreed-upon nomenclature for the various types of gambling disorders. This is partly because researchers, psychiatrists, other treatment care clinicians, and public policy makers frame questions about gambling differently depending on their disciplinary training, specialization, and world view. The absence of a standard nomenclature has also contributed to a wide range of definitions and treatments for gambling disorders.

The defining characteristics of pathological gambling include damage or disruption to personal, social, or occupational functioning; preoccupation with gambling; and loss of control of gambling behavior. Until recently, it was viewed as an underlying condition affecting other disorders and was treated as a subtype of substance dependence in the Diagnostic and Statistical Manual of Mental Disorders (DSM). The DSM-III criteria were heavily criticized for their unidimensionality and emphasis on external consequences and were later replaced by a set of criteria that more closely mirrors those used to diagnose addiction to substances.

The best way to overcome a problem with gambling is to seek help. Counseling can help individuals understand the underlying issues that are causing them to gamble and consider alternatives, such as learning to relieve unpleasant feelings in healthier ways (e.g., exercising, spending time with friends who do not gamble, or practicing relaxation techniques). Support groups for gamblers are another helpful resource and there are national and state gambling helplines as well as a self-help group for families called Gam-Anon. Inpatient or residential programs are available for those who are unable to control their gambling habits without round-the-clock support. Medications are not currently approved to treat gambling disorders, but research has shown that some medications can help treat co-occurring conditions such as depression or anxiety.