This chapter begins with a review of published studies reporting school-based interventions. The following sections use data from the Sussex and London studies to consider intervention strategies in the light of its findings. The first factor considered is smoking prevalence and adolescents' knowledge of the effects of smoking. Later sections examine the influence of families, friends, beliefs, attitudes towards the body, the effects of stress and coping, social identities and social settings on smoking behaviour. The contribution of the qualitative findings is considered in subsequent sections. Finally, developmentally based school interventions are proposed.