Diabetes Mellitus (DM) is a chronic, progressive metabolic disorder characterized by persistent hyperglycemia, arising from defects in insulin secretion, insulin action, or both. Affecting millions globally, DM is a significant public health challenge contributing to high morbidity and mortality rates. This review article explores the classification of DM, highlighting the differences between Type 1, Type 2, and gestational diabetes, alongside rarer forms. Key risk factors such as genetic predisposition, obesity, age, and lifestyle choices are discussed, underlining their contribution to the rising global incidence. The article also delves into the complications associated with uncontrolled diabetes, including microvascular and macrovascular issues, as well as the psychological burden. Modern diagnostic techniques, including the Hemoglobin A1c test and oral glucose tolerance test, are explained. Treatment strategies, from lifestyle interventions to pharmacological treatments like insulin therapy and GLP-1 receptor agonists, are presented to illustrate the comprehensive management of the disease. The review concludes by emphasizing the importance of early diagnosis and long-term glucose control to prevent complications and improve patient outcomes.