This chapter provides a summary of the prevalence rates, patterns of comorbidity, treatment rates and impact and consequences of mood disorder subtypes in adults and youth. The emergence of evidence of prevalence of mood disorders in community-based samples during the past decade demonstrates that BPS is far more common than earlier estimated. Recent studies of the BPS in youth indicate that the peak prevalence of BPS emerges in late adolescence and early adulthood. Comorbidity between both BPD and MDD with other mental disorders is pervasive, with the greatest co-occurrence for anxiety disorders and substance use disorders. Despite a large increase in the proportion of people with mood disorders who receive professional treatment, there is still a large gap between those with impairing mood disorders who remain untreated. The global burdens of both BPD and MDD are equivalent to that of many other common chronic diseases, and there is tremendous impact of both subtypes of mood disorders at both the individual and societal levels.