Diabetes mellitus is one of the most prevalent non-communicable diseases worldwide and represents a significant public health challenge. Characterized by chronic hyperglycemia resulting from defects in insulin secretion, insulin action, or both, diabetes affects individuals of all ages and socioeconomic backgrounds. The rapid increase in diabetes prevalence is associated with urbanization, sedentary lifestyles, unhealthy dietary patterns, and population aging. This article examines the definition, historical background, classification, causes, symptoms, diagnosis, complications, treatment, prevention, and global impact of diabetes mellitus. It also highlights current challenges in diabetes management and emphasizes the importance of public health interventions in reducing the burden of the disease.