Although it is becoming increasingly clear that B cells play important roles in multiple sclerosis (MS) pathogenesis, it is incompletely understood how they contribute. The purpose of this review is to provide an overview of the current knowledge about B cells in MS taking into account MS heterogeneity. The efficacy of B cell-depleting therapies has provided strong evidence for the involvement of these cells in MS pathogenesis. Although pathogenic antibodies were found in some MS patients, the observation that plasma cells and antibodies remain largely unchanged after B-cell depletion suggests that B cells are involved in MS by other mechanisms than antibody production. MS is an autoimmune disease, in which T and B cells play a crucial role. B cells can be involved in MS by different mechanisms such as presentation of antigens to T cells, transport of antigens from tissues to secondary lymphoid organs, secretion of pro-inflammatory or anti-inflammatory cytokines and in a subgroup of patients also production of pathogenic antibodies. As several B-cell/antibody-directed therapies are available, it is important to understand how these different functions of B cells and antibodies vary among patients in order to identify which could benefit best from the different therapies.