Gambling is the wagering of something of value (money, goods, or services) on an event that has at least some element of chance and the intention of winning. Games of chance, including lotteries, are the largest source of legal gambling in the world. Gambling can also include a variety of activities that involve consideration, risk, and a prize, such as bingo, sports betting, buying lottery or scratch tickets, and office pools.

The psychological factors that influence gambling can be complex and vary between individuals. For example, research has shown that some people are genetically predisposed to thrill-seeking behaviours and impulsivity, while others have difficulty controlling their emotions or weighing risk against reward. Some people gamble as a way to relieve unpleasant feelings, such as loneliness or boredom, or to distract themselves from painful or stressful experiences. For some people, the activity can become addictive.

Compulsive gambling tends to run in families and symptoms can begin during adolescence or early adulthood. It can be triggered by trauma or social inequality and is more common among men than women. Symptoms can also be aggravated by depression or other mental health problems and may develop in conjunction with alcohol use disorders. Despite its high rates of prevalence, only one in ten people with gambling disorder seek treatment. The understanding of problem gambling has undergone a profound change from its being viewed as a moral flaw to being considered an addiction similar to substance abuse. This shift has been reflected in the various editions of the Diagnostic and Statistical Manual of Mental Disorders, or DSM, published by the American Psychiatric Association between 1980 and 1994.