Rheumatoid Arthritis (RA) Moderate to Low Disease Activity Study

Treatment period starts with a 24-week, double blind, placebo-controlled, randomized period followed by an open label phase until week 52. In the double blind phase eligible patients will be randomized via an Interactive Voice Response System (IVRS) in a 1:1 ratio to receive either certolizumab pegol (400 mg at Weeks 0, 2 and 4, followed by 200 mg every two weeks) or placebo up to and including Week 22. All patients will continue to receive their Disease Modifying AntiRheumatic Drugs (DMARDs) therapy established before study entry until Week 52. At Week 24, patients will not receive any injection but will be evaluated: * Non-remitters at Week 24 (patients who did not achieve remission at both Week 20 and Week 24) will be discontinued from the study and may be given the opportunity to enter in an open-label follow-up trial, C87080 \[NCT00843778\], with certolizumab pegol. * Remitters (i.e. patients who achieved remission as measured by Clinical Disease Activity Index (CDAI) at both Week 20 and Week 24) will stop their randomized treatment (certolizumab pegol or placebo) and be followed up until Week 52. Remitters who flare up (CDAI ≥11 confirmed at two consecutive visits four weeks apart) between Week 24 and Week 52 will be re-treated with the same dosing regimen of certolizumab pegol (3 administrations of 400mg, given every 2 weeks, followed by 200 mg given every other week) up to and including Week 50. Remitters who flare up between Week 24 and Week 52 and complete 52-week study period will be allowed to enter open label follow up trial at Week 52.