Autoimmunity results from abnormal B‐ and T‐cell recognition of self‐antigens, which leads to autoantibody production in many cases. Autoantibodies produced by B‐cell‐derived plasma cells provide diagnostic markers for autoimmunity but also contribute significantly to disease pathogenesis. As discussed in this review, the therapeutic benefit of depleting B cells in mice and humans has refocused attention on B cells and their role in autoimmunity beyond autoantibody production. B cells specifically serve as cellular adjuvants for CD4⁺ T‐cell activation, while regulatory B cells, including those that produce interleukin‐10 (B10 cells), function as negative regulators of inflammatory immune responses. The emerging picture is that B cells, autoantibodies, and T cells are all important components of abnormal immune responses that lead to tissue pathology unique to each autoimmune disease, with their relative contributions changing during disease progression. Autoimmune diseases where B‐cell functions are closely correlated with disease activity include systemic lupus erythematosus, rheumatoid arthritis, scleroderma, type 1 diabetes, and multiple sclerosis. Understanding the overlapping roles of B cells as mediators of autoimmune disease will facilitate the development of more precisely directed therapies and combination therapies with broader clinical efficacy than current depletion strategies that remove all B cells.