Previous epidemiological studies suggest that mood and anxiety disorders are highly prevalent among the general population and are a leading cause of disease burden. Furthermore, mental health disorders have major economic implications for wider society in terms of elevated healthcare costs as well as reduced productivity among those who suffer these conditions. The central aim of the current thesis was to undertake the first comprehensive investigation of the economic and social burden of mood and anxiety disorders in Northern Ireland, based on validated diagnostic estimates. This was achieved by 1) an examination of the prevalence and correlates; 2) and investigation of levels of service use; 3) an estimation of the societal economic costs; and 4) an examination of the experience, mental health impact and economic costs of psychological trauma. Analyses were based primarily on data from the Northern Ireland Study of Health and Stress, the largest epidemiological study of mental health in Northern Ireland based on validated diagnostic criteria. A range of additional data sources were drawn upon to produce economic cost-of-illness estimates. All analyses were implemented using Stata. The current thesis clearly demonstrates that mood and anxiety disorders represent a substantial public health burden in Northern Ireland. Prevalence rates are among the highest of all estimates produced around the world. Civil conflict has undoubtedly contributed to high levels of mental ill health, manifested by the rates of PTSD and other trauma-related disorders. Despite the elevated burden of mood and anxiety disorders, the majority of individuals do not seek help. Cost-of-illness estimates suggest that these disorders are associated with an annual economic burden of around £1.45 billion and £1.35 billion respectively. Evidence presented throughout the current thesis provides a robust evidence-base to inform the provision of effective services for these conditions and allocation of resources to those most in need.