Diabetes mellitus (DM) is a chronic medical condition that continues to increase in prevalence. Complications of DM, including diabetic ketoacidosis and hyperglycemic hyperosmolar state, often present in the emergency department requiring emergent management. Prompt assessment, diagnosis, evaluation of laboratory values, treatment, monitoring, and strict follow-up education are essential to the successful management of this complex disease. Common medications and management strategies are key elements to control DM. This article presents an overview of DM, including its prevalence, pathophysiology, presentations, and management.