B cells are vital in renal transplantation. B2 cells are part of the adaptive immune system. Activated B cells mature into plasma cells or memory B cells: their life spans can be prolonged by niches. B cells have a wide variety of functions: antibody production, antigen presentation, cytokine production and shaping of the splenic architecture. These functions play a vital role in graft rejection, both T cell-mediated rejection and antibody-mediated rejection. Markers of B cell activity include intragraft B cell infiltration, C4d deposition and circulating donor-specific antibodies. Many therapeutic options target B cells or plasma cells. As greater understanding is gained of their appropriate use, and new agents are developed, we should see prolonged graft survival and reduced graft rejection.