Women are on average twice as likely as men to experience depression and anxiety disorders. Several explanations have been proposed to explain these gender disparities. However, few studies have examined the possibility that the gender difference in depression and anxiety prevalence, and the explanatory factors involved, vary across the life course. This thesis describes the pattern of distribution for gender differences in depression and anxiety levels across the adult lifespan, and evaluates the role of potential psychosocial risk factors at particular life stages. Analyses were undertaken using the first and second waves of the Personality and Total Health (PATH) Through Life study. This study collects data on three narrow-aged cohorts living in the Canberra and Queanbeyan region (Australia) every four years. At Wave 1, participants were aged 20- 24, 40-44 and 60-64. The outcome measures used in this thesis were the Goldberg Depression and Anxiety Scales. Across the three PATH cohorts, women experienced higher levels of depression and anxiety than did men. However differences were most prominent in the youngest age group. Latent variable modelling showed that for each age group, the gender difference in levels of depression and anxiety could not be attributed to gender-biased items. Two pathways to the gender disparity in depression and anxiety levels were explored. First, multivariate mediation analyses identified gender differences in exposure to potential psychosocial risk factors. Second, Ordinary Least Squares (OLS) regression identified gender differences in vulnerability or susceptibility to potential psychosocial risk factors. Women of all age groups were more exposed than men to childhood adversity, low mastery, high behavioural inhibition, rumination, neuroticism, poor health and interpersonal problems, factors that were associated with greater depression and anxiety. They were also more vulnerable than men to depression and anxiety if they had experienced negative events involving social networks or were recently married, or if they had poor cognitive function or low mastery. Age comparisons suggested that stress in domestic relationships and responsibilities were particular vulnerabilities for young women, and that middle aged women were specifically susceptible to poor social support and behavioural inhibition. No specific vulnerabilities emerged for older women. While the focus of this thesis was identifying potential risk factors that might explain the preponderance of symptoms for women, the analysis techniques adopted also provided information on potential risk factors relevant to men. The findings showed that men were more exposed to employment problems than women, and were more vulnerable to alcohol abstinence, aggression and problems at work. For young men, unemployment was a particular vulnerability, as were domestic responsibilities for middle aged men, and poor health and low family support for older men. Overall, the potential psychosocial risk factors identified for depression were similar to those identified for anxiety. This thesis confirms that a lifespan perspective is important when describing gender differences in depression and anxiety, and identifying associated risk factors. It also demonstrates that the roles played by potential risk factors, can be investigated effectively using the frameworks of exposure and vulnerability. Information regarding levels of depression and anxiety amongst subgroups such as gender and age group, as well as the risk factors most relevant to these subgroups, is important for understanding the development of anxiety and depression, and in framing potential prevention interventions.