Body image disturbance and unhealthy dieting in adolescent females are areas of particular concern for mental health professionals, teachers, and parents. Many theories have been developed to explain body image disturbance and unhealthy dieting, in which sociocultural pressure and interpersonal influences are prominent. However, there is still no clear understanding of how these influences interrelate or how they impact upon body image disturbance and unhealthy dieting. In addition, very little research has been conducted in New Zealand examining the role of such pressures, or investigating body image or dieting. This thesis explores the role of social evaluation, incorporating both sociocultural and interpersonal variables, in the development of body image disturbance and unhealthy dieting in New Zealand adolescent females. The research programme incorporated three studies, firstly focus group discussions, followed by a survey study, and finally an experimental paradigm. Focus group discussions were conducted with female teenagers to explore their conceptualisations of dieting, and to identify areas of social evaluation that were of particular import to New Zealand teenagers. Need for approval, appraisal sensitivity, media influence, appearance evaluation, and peer comparison emerged as dominant themes in the teenagers discussions. The second study extended the focus group data through a survey with 190 female high school students about the social evaluation themes identified in the focus group discussions as well as body image disturbance, unhealthy dieting, and low mood. Structural equation modelling was utilised to test a model of interrelationships between these variables. The survey study established that there were indirect and direct relationships between the variables of social evaluation, body image disturbance, unhealthy dieting, and low mood. Specifically appearance-related feedback and appearance-related comparison emerged as having pivotal roles in the model of interrelationships. The final stage of the research programme further extended the findings of the focus group discussions and the survey study by using an experimental paradigm. A pilot study was conducted with 33 high school students to ensure that the methodology of a mood induction procedure intended to reflect negative appearance-related feedback and negative appearance-related comparison was powerful enough to elicit changes in body image and negative affect. For the final study, a further 33 female high school students participated in the imaginal mood induction procedure and completed questionnaires assessing appraisal sensitivity and sociocultural ideals. Repeated measures analyses demonstrated that participants' body image disturbance increased after exposure to the imagined social situations. Negative affect also increased after the imaginal mood induction procedure. Peer feedback had a stronger influence on levels of anger, happiness, and inferiority/'stinkness'. Unexpectedly, dispositional levels of appraisal sensitivity and internalisation of the thin-ideal did not moderate the effects of the mood induction procedure on participants ratings of body image disturbance. This research programme demonstrated that social evaluation has an important and influential role in the development of body image disturbance and unhealthy dieting in female adolescents. This thesis highlights the importance of considering how the interrelationships between sociocultural and interpersonal variables affect body image disturbance. The research programme also provides many opportunities for future research and clinical investigations in the areas of models of interrelationships, body image disturbance, and unhealthy dieting.