Diabetes and obesity are chronic medical conditions that place a substantial health and economic burden on people, family members, and the global health-care system. Diabetes has been identified as the sixth leading noncommunicable cause of death by the Global Burden of Diseases, Injuries, and Risk Factors Study 2021. It is also a contributing factor to the first and second leading causes of death in ischemic heart disease and stroke, respectively, as well as being estimated to result in over 1 trillion dollars in health-care expenses by 2045 [1, 2]. Obesity is estimated to affect 16% of the global adult population, and 42.4% of US adults [3–5]. Significant disparities in care exist across the globe and within individual countries due to the impact of social determinants of health [1]. This chapter will provide an overview of the epidemiology and pathophysiology of each general category of diabetes, with a specific focus on type 2 diabetes due to its high prevalence, as well as the disease of obesity.