Explores the issues around establishing causality regarding gambling and associated social and economic problems, particularly those related to negative externalities. Also considers economic transfers and redistribution effects. Aims to propose and discuss the next steps required to more effectively estimate the costs of the impacts of gambling. Describes externalities induced or caused by gambling. Discusses, from an epidemiological perspective, the criteria by which causality is ascertained. Presents a simple model of to classify impacts of gambling. Reviews relevant literature. Concludes with recommendations to estimate the societal costs of gambling.