The main theme of the thesis was to examine the relationship between social influences and adults’ eating behaviour, in particular how social identity affects the norm influence on eating behaviour. Chapter One describes the general background and evaluates the research literature. Chapter Two reports the results of a longitudinal investigation of the relationship between perceived eating norms and self-reported food consumption among a student population. Chapter Three presents a pair of online studies that tested whether social norms predict eating and whether there is an interaction between norm effects and social identity in both a community and student population. Chapter Four presents the results of two laboratory-based experiments that examined the moderating effect of social identity on the relationship between social norm messaging and healthy /unhealthy food consumption using a remote-confederate design. Chapter Five reports the results of a laboratory study that examined the effect of manipulating social identity on social norm enhancement of eating behaviour. Chapter Six reviews all findings, reflects on the importance of completed work, and concludes that social influences on eating are robust and social identity plays a moderating role. The findings have implications for the development of norm-identity based interventions in promoting healthier dietary habits.