Type 1 diabetes mellitus (T1DM) is an autoimmune disorder in which the immune system mistakenly destroys insulin-producing beta cells in the pancreas. This results in absolute insulin deficiency, leading to chronic hyperglycemia. It commonly presents in childhood or adolescence, although it can develop at any age. The exact cause is multifactorial, involving genetic predisposition (e.g., HLA-DR3/DR4) and environmental triggers such as viral infections. Classic symptoms include polyuria, polydipsia, weight loss, and fatigue. Without insulin therapy, Type 1 diabetes is life-threatening and can lead to diabetic ketoacidosis (DKA). Lifelong exogenous insulin administration is essential, delivered via injections or insulin pumps. Innovations such as continuous glucose monitors (CGMs) and hybrid closed-loop systems (artificial pancreas) have significantly improved glucose control and quality of life. Despite these advances, individuals remain at risk for microvascular and macrovascular complications. Patient education, carbohydrate counting, and psychological support are integral parts of comprehensive care. Early diagnosis, tight glycemic control, and ongoing research into beta-cell preservation and immune therapies remain pivotal to improving outcomes in T1DM.