Type 2 diabetes mellitus has become an epidemic, and virtually no physician is without patients who have the disease. Whereas insulin insensitivity is an early phenomenon partly related to obesity, pancreas β-cell function declines gradually over time already before the onset of clinical hyperglycaemia. Several mechanisms have been proposed, including increased non-esterified fatty acids, inflammatory cytokines, adipokines, and mitochondrial dysfunction for insulin resistance, and glucotoxicity, lipotoxicity, and amyloid formation for β-cell dysfunction. Moreover, the disease has a strong genetic component, but only a handful of genes have been identified so far: genes for calpain 10, potassium inward-rectifier 6·2, peroxisome proliferator-activated receptor γ, insulin receptor substrate-1, and others. Management includes not only diet and exercise, but also combinations of anti-hyperglycaemic drug treatment with lipid-lowering, antihypertensive, and anti platelet therapy.