A Study Comparing Upadacitinib (ABT-494) to Placebo and to Adalimumab in Adults With Rheumatoid Arthritis Who Are on a Stable Dose of Methotrexate and Who Have an Inadequate Response to Methotrexate

* Adult male or female, at least 18 years old. * Diagnosis of RA for greater than or equal to 3 months. * Subjects must have been on oral or parenteral methotrexate (MTX) therapy greater than or equal to 3 months and on a stable prescription of greater than or equal to 15 to 25 mg/week (or greater than or equal to 10 mg/week in subjects intolerant of MTX at doses greater than or equal to 12.5 mg/week) for at least 4 weeks prior to the first dose of study drug. In addition all subjects should take a dietary supplement of folic acid or folinic acid throughout the study participation. * Meets the following minimum disease activity criteria: greater than or equal to 6 swollen joints (based on 66 joint counts) and greater than or equal to 6 tender joints (based on 68 joint counts) at Screening and Baseline Visits. * At least one of the following at Screening: greater than or equal to 3 bone erosions on x-ray OR greater than or equal to 1 bone erosion and a positive rheumatoid factor OR greater than or equal to 1 bone erosion and a positive anti-cyclic citrullinated peptide autoantibodies. * Subjects with prior exposure to only one biological disease-modifying anti-rheumatic drugs (bDMARD) (except adalimumab) may be enrolled (up to 20% of total study population) if they have documented evidence of intolerance to the bDMARD or limited exposure (less than 3 months), but required washout periods need to be satisfied. * Except for MTX, subject must have discontinued all conventional synthetic disease-modifying anti-rheumatic drugs (csDMARDs).

* Prior exposure to any Janus kinase (JAK) inhibitor (including but not limited to tofacitinib, baricitinib, and filgotinib). * Subjects who have been exposed to adalimumab or who are considered inadequate responders to bDMARD therapy as determined by the Investigator. * History of inflammatory joint disease other than RA. History of secondary Sjogren's Syndrome is permitted.