The Interdisciplinary Study of Inequalities in Smoking (ISIS) is a cohort study investigating the joint effects of residents’ socio-demographic characteristics and neighbourhood attributes on the social distribution of smoking in a young adult population. Smoking is a behaviour with an increasingly steep social class gradient; smoking prevalence among young adults is no longer declining at the same rate as among the rest of the population, and there is evidence of growing place-based disparities in smoking. ISIS was established to examine these pressing concerns. The ISIS sample comprises non-institutionalized individuals aged 18–25 years, who are proficient in English and/or French and who had been living at their current address in Montréal, Canada, for at least 1 year at time of first contact. Two waves of data have been collected: baseline data were collected November 2011-September 2012 (n = 2093), and a second wave of data was collected January-June 2014 (n = 1457). Data were collected from respondents using a self-administered questionnaire, developed by the research team based on sociological theory, which includes questions concerning social, economic, cultural and biological capital, and activity space as well as smoking behaviour.