Abstract: Graves' disease (GD) is the most common cause of hyperthyroidism. GD is an endocrine autoimmune disorder caused by the presence in serum of TSH receptor-stimulating autoantibodies (TRAb) that induce the overproduction of 3,3',5'-triiodo-L-thyronine (T3) and L-thyroxine (T4) and enlargement of the thyroid gland. GD is also often accompanied by autoantibodies against other thyroid antigens such as thyroglobulin and thyroid peroxidase. The prevalence of GD is around 1-1.5 % worldwide, with an incidence of 20 to 50 new cases per 100,000 inhabitants per year with a considerably higher frequency in women than in men. In addition to hyperthyroidism, extrathyroidal manifestations including orbitopathy, thyroid dermopathy, and acropachy are frequently associated with GD. Genetic factors (such as HLA-DR3, CD40, CTLA-4, PTPN22, FOXP3, and CD25) and environmental and endogenous factors (such as age, emotional stress, smoking, female sex, pregnancy, bacterial and viral infections, and some drugs) contribute to the development of GD. Although the pathogenesis of GD has been better understood, directed treatments against the molecular mechanisms are lacking. Therapies for GD are presently based upon antithyroid drugs, but due to the high rate of recurrence in hyperthyroidism, ablation of the thyroid by either radioiodine treatment or surgical thyroidectomy is the only treatment available. In the present chapter, we provide updated knowledge on the epidemiology and etiopathogenesis of GD.