This overview of the thyroid autoimmunity in human presents the various facets of a very common pathology. Focus is rather on fundamental than clinical aspects, although some specific clinical situations are discussed. Epidemiology, pathophysiology and pathology of AITD are detailed. One of the peculiarities of AITD is that they express two opposed phenotypes, hypothyroid thyroiditis and hyperthyroid Graves’ disease. The latter is characterised by the presence of a unique type of autoantibodies, the anti-TSH receptor antibodies. Those are capable to activate the TSH receptor leading to the gland hypertrophy and hyperfunction. On the contrary, the autoimmune thyroiditis processus progressively and slowly tends to the necrosis/apoptosis of thyroid cells and their functional impairment. Other forms of autoimmune thyroiditis, postpartum thyroiditis and silent thyroiditis are also described. This review, which is not exhaustive, aims at providing a wide scope on the AITD, a basis from which the interested reader or the specialist will be able to find routes towards deeper knowledge.