This was a multinational, multicenter, randomized, double-blind, 2-arm, parallel-dosing designed study. The treatment period was 12 months. Eligible participants were randomized to 1 of 2 treatment groups: abatacept fixed dose approximating 10 mg/kg (based on participant's body weight; 500 mg for participants weighing < 60kg; 750 mg for participants weighing 60 to 100 kg; and 1 gram for participants weighing > 100 kg, monthly) or placebo intravenous (IV) infusion. All participants continued their background therapy(ies) for rheumatoid arthritis (RA) (non-biologic or biologic disease-modifying drugs [DMARDs], or combination) throughout the double-blind treatment period. Double-blind study medication (abatacept or placebo) was administered on Days 1, 15, 29, and every 28 days thereafter, for a total of 14 doses.