This is a Phase 3 multicenter study that includes two periods. Period 1 is a 12-week, randomized, double-blind, parallel-group, placebo-controlled period designed to compare the safety and efficacy of upadacitinib versus placebo for the treatment of signs and symptoms of participants with moderately to severely active RA who are on a stable dose of csDMARDs and have an inadequate response to csDMARDs. Period 2 is an open label 52 week extension period to evaluate the long-term safety, tolerability, and efficacy of upadacitinib in participants with RA who have completed Period 1.