 This Phase 3 study is intended to provide evidence of the efficacy and safety of CP 690,550 when dosed 5 mg and 10 mg twice a day as monotherapy in adult patients with moderate to severe Rheumatoid Arthritis. It is intended to confirm the benefits of CP-690,550 in improving signs and symptoms and physical function that were observed in the Phase 2 Rheumatoid Arthritis studies. 