This portfolio thesis comprises three parts: a systematic literature review, a quantitative empirical paper and supporting appendices. Part One is a systematic review of the literature regarding the role that social comparison plays in the relationship of social networking site use and wellbeing. This review builds upon evidence suggesting that social network site use impacts positively and negatively upon well-being, aiming to understand possible underlying processes. The psychological impacts of social comparison on social networking sites are also considered in the empirical investigation presented in the paper in Part Two. The empirical study focuses specifically upon appearance comparisons made when using social networking sites and considers the impacts upon body satisfaction. Furthermore, the empirical paper considers whether compassion is protective against the negative impacts on body image of appearance comparison when social networking. The empirical study used quantitative methodology and questionnaire data from social network site users to explore these relationships. Part Three comprises of appendices, including reflective and epistemological statements.