Rheumatoid arthritis (RA) is the most common chronic inflammatory disorder of the musculoskeletal system that may cause permanent joint damage. The disease has a major impact on the quality of life of affected individuals, costs for the health care system, and society. Currently, no curative treatment is available, and patients are subjected to a prolonged course of treatment. Due to their role in the pathogenesis of RA, B cells have become an attractive target for therapy. Rituximab (Mabthera®/Rituxan®) is a therapeutic monoclonal antibody against CD20 expressed on B cells, which is effective in depleting B cells and approved worldwide for the treatment of RA. Rituximab was shown to be highly beneficial in decreasing clinical symptoms, safe, and well tolerated. However, clinical experience revealed that approximately 30-40% of RA patients do not respond to it. Given the destructive nature of RA, the risk of adverse effects, and considerable costs for therapy, there is a strong need to make predictions on the clinical outcome before the start of therapy. Since nearly all treated patients experience an effective depletion of circulating B cells, questions have been raised concerning the mechanism of action. In this review, novel developments, in particular the findings on the role of the interferon system, will be highlighted. This may add new and important information to our understanding of the mechanism that underlies the clinical outcome of rituximab treatment and may lead to the identification of biomarkers to predict the response.