The occurrence of factor VIII (FVIII) inhibitors is one of the major complications of the treatment of haemophilia A. We present this review as a description of the major players of the antiFVIII immune response, with particular emphasis on the nature and properties of the different antiFVIII antibodies, their mechanisms of action in inhibiting FVIII activity, their potential neutralization by anti-idiotypic antibodies, and the importance of the T cell in participating in the induction of FVIII inhibitors. We briefly conclude on the avenues that remain to be explored in order to establish efficient therapeutic approaches aimed at eliminating FVIII inhibitors in patients with haemophilia A.