Substance use behaviours have been viewed as the end products of a combination of influences. Numerous theories for working with substance use behaviour utilizing a multi-systemic approach have been proposed. In this project, an effort was made to control for limitations and problems that have often beset previous studies utilizing such an approach. The overall objective of the current project was to test, using a multi-systemic approach, the ability of the family socialization framework to explain the development of substance use patterns in youth and young adults. The central hypothesis of this project was that family socialization factors (contextual factors) affect and predict the development of an offspring’s personality (individual factors) and substance use behaviour. The behavioural genetic approach (i.e., the adoption design) was utilized to examine the genetic and environmental impacts on associations between factors. This project used secondary data analyses of general population data to examine the links between aspects of the family environment, personality, and substance use patterns. The Vancouver Family Survey data set used here contained information on fathers, mothers, and offspring from 405 families (328 biological and 77 adoptive) at two points in time. The development of personality and substance use behaviours over time, and associations with family socialization factors, were examined through three studies. Study 1 focused on the associations between offspring’s perspectives of fathers’ and mothers’ parental socialization and offspring’s polysubstance use. Study 2 investigated the development of addiction-prone personality characteristics and the predictive effects of family socialization and demographic variables on these characteristics. Study 3 explored the subscales of the Addiction-Prone Personality scale: impulsivity/recklessness, sensation seeking, negative view of self, and social deviance proneness. The descriptive characteristics of each subscale and changes in subscale scores over time were investigated. Also examined were transgenerational associations on these subscales, and potential relationships between personality subscales and choice of substance. The results of this project suggest that family socialization may be linked with both substance use behaviour and personality development over time. Nurturing family socialization is negatively associated with the development of addiction-prone personality characteristics. It is also negatively associated with the development of substance use behaviours. These results are consistent with previous studies utilizing a family socialization framework. The findings supporting the family socialization framework are very encouraging for the field of child, youth, and family-related practice. Some of the limitations of the current project, implications of the findings, and future research directions are discussed. / Graduate