Diabetes mellitus is a complex metabolic disorder associated with acute and chronic complications that significantly increase morbidity and mortality worldwide. Acute complications, including diabetic ketoacidosis and hyperosmolar hyperglycemic state, arise primarily from insulin deficiency and counterregulatory hormonal imbalances. Chronic complications—such as retinopathy, nephropathy, neuropathy, and macrovascular disease—are driven by prolonged hyperglycemia, oxidative stress, inflammation, and endothelial dysfunction, resulting in progressive organ damage. These complications are further compounded by gastrointestinal manifestations and impaired wound healing, which negatively impact quality of life. Prevention and management strategies emphasize early detection, lifestyle modification, optimal glycemic control, and the use of novel therapeutic agents including SGLT2 inhibitors and GLP-1 receptor agonists, which have demonstrated cardiovascular and renal benefits. Understanding the underlying pathogenesis of diabetic complications is essential for guiding effective prevention and treatment strategies. This review highlights the mechanisms, clinical manifestations, and preventive approaches for diabetes complications, aiming to inform comprehensive patient care and reduce the global burden of the disease.