Although it is widely believed that one of the key factors influencing whether an adolescent smokes or not is the smoking behaviour of his or her peers, empirical evidence on the magnitude of such peer effects, and even on their existence, is mixed. This existing evidence comes from a range of studies using a variety of country-specific data sources and a variety of identification strategies. This paper exploits a rich source of individual level, school-based, survey data on adolescent substance use across countries - the 2007 European Schools Survey Project on Alcohol and Other Drugs - to provide estimates of peer effects between classmates in adolescent smoking for 75,000 individuals across 26 European countries, using the same methods in each case. The results suggest statistically significant peer effects in almost all cases. These peer effects estimates are large: on average across countries, the probability that a 'typical' adolescent smokes increases by between.31 and.38 percentage points for a one percentage point increase in the proportion of classmates that smoke. Further, estimated peer effects in adolescent smoking are stronger intra-gender than inter-gender. They also vary across countries: in Belgium, for example, a one percentage point increase in reference group smoking is associated with a.16 to.27 percentage point increase in own smoking probability; in the Netherlands the corresponding increase is between.42 and.59 percentage points. © 2011 Elsevier Ltd.