General population surveys show that gambling is prevalent in many high-income countries. Gambling is not an exclusive activity that only a few people engage in; it has become a popular recreational pursuit, especially in countries where it is legal, accessible, and commercialized. The epidemiological and clinical research reviewed in this chapter indicates that gambling problems tend to be concentrated, though not exclusively, in the most vulnerable and disadvantaged groups, including ethnic minorities, the homeless, the unemployed, the mentally ill, alcohol and drug users, and those who have lower incomes and socio-economic status. Gambling transfers wealth from the most frequent gamblers to owners of the operating companies, to the government authorities, and to the beneficiaries of direct contributions to “good causes”.