ACP-196 Versus Placebo in Subjects With Rheumatoid Arthritis on Background Methotrexate

Main Inclusion Criteria: * Diagnosis of RA according to the 2010 ACR/EULAR Classification Criteria . * Must be on a stable MTX dose (7.5 to 25 mg/week) * Subjects must be able to read and understand the consent form, complete the study-related procedures, and communicate with the study staff. * Are willing and able to adhere to the study visit schedule, and understand and comply with other protocol requirements. Main Exclusion Criteria: * Prior malignancy, except for adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer, or other cancer from which the subject has been disease free for ≥ 5 years. * A life-threatening illness, medical condition or organ system dysfunction which, in the investigator's opinion, could compromise the subject's safety, interfere with the absorption or metabolism of ACP-196, or put the study outcomes at undue risk. * Subjects who have taken any investigational drug within the previous 30 days before randomization. * Use of all other synthetic disease-modifying antirheumatic drugs (DMARDS) such as but not limited to leflunomide, azathioprine, cyclosporine, penicillamine or gold salts within 8 weeks of randomization. * Use of etanercept, anakinra, tofacitinib within 4 weeks of randomization. * Use of abatacept, humira, infliximab, or tocilizumab within 8 weeks of randomization.