Human IgG receptors are very heterogeneous and we currently distinguish three Fc gamma receptor classes specifying at least 12 receptor isoforms. On top of this complexity, Fc gamma R are further found to differ between different individuals. Polymorphisms have been identified for all three Fc gamma R classes. The best-studied ones represent allelic variation of Fc gamma RIIa (CD32) and Fc gamma RIIIb (CD16). The Fc gamma RIIa polymorphism is now considered to be a heritable risk factor for autoimmune and infectious diseases, and support for a relevant role of the IIIb polymorphism has also been obtained. A detailed analysis of the exact contribution of each of these Fc gamma R polymorphisms in relation to previously implicated risk factors should unravel the pathophysiological importance of Fc gamma R polymorphisms in the near future.