Normally the immune system does not produce pathogenic antibodies to autologous antigens, due to induction of self-tolerance in both the T and B lymphocyte repertoires. The aim of this paper is to review the evidence for self-tolerance within the B cell repertoire, and the range of possible mechanisms responsible for it. In practice, the mechanism of B cell tolerance to autologous antigens in vivo remains controversial, and may in fact vary (depending on the nature of the self antigen and the properties of the self-reactive B cell. Recent work in transgenic mouse models of B cell tolerance has helped to assimilate the numerous and sometimes disparate findings from other models, firstly by allowing direct visualization of the fate of self-reactive B cells in vivo, and secondly, by enabling systematic genetic changes to be made either in the self antigen or in the self-reactive B cell.