Alcohol, tobacco, illegal drugs and psychoactive medication (mis)use are associated with a higher likelihood of developing several diseases, (traffic) injuries and crimes. These substances reduce quality of life and increase the health care and law enforcement costs, productivity losses, etc. Consequently, the social and economic impact of substances on society is substantial. The SOCOST study estimates for the first time social costs for alcohol, tobacco, illegal drugs and psychoactive medication in Belgium for the year 2012. This cost-of-illness study presents the direct costs, the indirect cost as well as the intangible costs related to substance (mis)use. This research was commissioned by the Belgian Federal Science Policy Office (BELSPO) in the framework of the Federal Research Programme Drugs. Two universities cooperated: Ghent University, Institute for International Research on Criminal Policy (IRCP) and the Vrije Universiteit Brussel, Interuniversity Centre for Health Economics Research (I-CHER). The research was conducted under supervision of prof. dr. Freya Vander Laenen, prof. dr. Koen Putman, prof. dr. Lieven Pauwels, prof. dr. Wim Hardyns and prof. dr. Lieven Annemans.