Much evidence supports the influence of family and peer factors as socialisation agents on young people’s drinking behaviour, commonly explained with adolescents’ modelling of peer and parental behaviours or with the reinforcement of alcohol use behaviour through parents and peers.As regards family factors, the research focus has almost exclusively been on parental influences. The present study seeks to expand the family perspective by including siblings as another important socialisation agent and to explore siblings’ influence in relation to those of parents and peers. The aim of the present proposal is to study the association of siblings’ alcohol use and adolescents’ drinking behaviour, and the impact of siblings’ drinking on facilitating or impeding factors of the parent-adolescent relationship and peer environment. The study further aims to investigate if associations expected for adolescent alcohol use can also be established for a more stringent measure of adolescent problem behaviour such as violence and delinquency. The study will use the Swiss data of the “European School Survey Project on Alcohol and Drugs (ESPAD, Hibell et al., 2004)” conducted in 2003. The sample consists of 7,193 12- to 18-year old students (mean age 14.6 years, SD=.97) and can be considered as representative for all 8th, 9th and 10th graders in public schools in Switzerland and in the main linguistic regions (German, French, and Italian speaking). The findings of the proposed study will help to better understand the importance of within-family processes and their interaction with peer factors in predicting adolescent alcohol use.Family-focused interventions such as the Strengthening Family Program (Spoth, Redmond & Shin, 2001) and Triple P (Sanders, Markie-Dadds & Turner, 2003) have shown positive impact on both parenting skills and adolescent problem behaviour, including adolescent alcohol use (Foxcroft et al., 2003; Moran, Ghate & van der Merwe, 2004). This study will contribute through its focus on complex interrelations between a multitude of family and peer factors that are modifiable and not yet considered in existing programmes, thus providing a more complete picture of risk factors and their interplay. Moreover, findings of this study will also benefit policy makers and practitioners in the field of health education by targeting the family as a valuable context for alcohol misuse prevention and subsequent resource allocation.