This thesis examined body dissatisfaction and body change behaviors among adolescent girls and boys from a biopsychosocial framework. The contribution of biological, psychological and sociocultural factors were examined in relation to body dissatisfaction, weight loss, weight gain and increased muscle tone behaviors among early adolescent girls and boys. In particular, pubertal maturation, body mass index (BMI), perception of body shape and size and psychological factors, such as depression, anxiety, ineffectiveness, self-esteem and perfectionism, were examined as possible factors that may precipitate or maintain body dissatisfaction and engagement in body change strategies. The sociocultural factors evaluated were the quality of family and peer relationships, as well as the influence of family and peers in predicting the adoption of specific body change strategies. The specific mechanisms by which these influences were transmitted were also examined. These included perceived discussion, encouragement and modelling of various body change strategies, as well as perceived teasing about body shape and size. A number of separate cross-sectional and longitudinal studies were conducted to examine the above relationships and identify the factors that contribute to weight loss, weight gain and increased muscle tone behaviors in adolescents. Study 1 examined the psychometric properties and principal components structure of the Bulimia Test Revised (BULIT-R; Thelen, Farmer, Wonderlich, & Smith, 1991) to assess its applicability to adolescent samples. Study 2 investigated the nature of body dissatisfaction and weight loss behaviors among 603 adolescents (306 girls and 297 boys) using a standardised questionnaire. This preliminary study was conducted to ascertain whether variables previously found to be relevant to adolescent girls, could also be related to the development of body dissatisfaction and weight loss behaviors among adolescent boys. Studies 3 and 4 described the development and validation of a body modification scale that measured weight loss, weight gain and increased muscle tone behaviors. Studies 5 and 6 were designed to modify an Excessive Exercise Scale developed by Long, Smith, Midgley, and Cassidy (1993) into a shorter form, and validate this scale with an adolescent sample. Study 7 investigated the factors that contribute to weight loss, weight gain and increased muscle among adolescent girls and boys both cross-sectionally and longitudinally (over one year). Structural equation modelling was used to examine associations among self-reported body dissatisfaction, body change strategies and a range of biological, psychological and sociocultural variables both cross-sectionally and longitudinally. Overall, the results suggested that both girls and boys experience body dissatisfaction and engage in a number of different body change strategies in order to achieve an ideal size. A number of gender similarities and differences were identified in the expression of body dissatisfaction and the adoption of body change strategies for both girls and boys. Girls were more likely than boys to report body dissatisfaction and engage in weight loss behaviors, while boys were more likely than girls to engage in weight gain and increased muscle tone behaviors. Generally, the same factors were found to contribute to weight loss, and more specifically, bulimic symptomatology, ad weight gain in both adolescent girls and boys. While a combination of biological, psychological and sociocultural factors contributed to bulimic symptomatology, only biological and psychological factors were found to contribute to weight gain in adolescents. The most notable gender differences were found in the model of increased muscle tone. Sociocultural and biological factors contributed to increased muscle tone behaviors in girls, while sociocultural and psychological factors were implicated in these behaviors in adolescent boys. With the exception of the model of increased muscle tone for boys, body dissatisfaction was a consistent factor in the adoption of body change behaviors. Consistent with previous investigations, the present thesis provides empirical support for the need to examine the etiology and maintenance of such concerns and behaviors from a multifaceted perspective.