IMPORTANCE: Chronic diseases have overtaken acute diseases, such as infections, as the major cause of premature mortality worldwide. Diabetes mellitus, a chronic degenerative metabolic disease, has reached epidemic proportions in the past 30 years, with worldwide prevalence approaching 400 million people. OBSERVATIONS AND ADVANCES: The epidemic is largely secondary to an increasing sedentary lifestyle and highly prevalent overweight and obesity contributing to the development of type 2 diabetes. Clinical research efforts have developed and demonstrated effective strategies for prevention, and the annual incidence of diabetes in the United States may be decreasing for the first time in 3 decades. The long-term complications of diabetes cause severe morbidity and mortality. Here too the means of reducing the burden of microvascular and cardiovascular disease have been proved. CONCLUSIONS AND RELEVANCE: Improved glycemic control and better management of other identified risk factors for the complications of diabetes and more effective treatment of cardiovascular disease and microvascular complications have resulted in a more optimistic outlook for people with diabetes. This review focuses on recent advances in diagnosis and management and the remaining challenges in the prevention and treatment of diabetes mellitus.