ESPOIR is a French multicenter cohort of patients with undifferentiated arthritis enrolled within six months of symptom onset, naive to disease-modifying antirheumatic drugs and corticosteroid therapy, and either having rheumatoid arthritis (RA) or being at risk for progression to RA. The cohort is sponsored by the French Society for Rheumatology (Société française de rhumatologie [SFR]). Between December 2002 and March 2005, 813 patients were enrolled at 14 regional university hospitals, with the participation of a network of community-based rheumatologists. The objective was to establish a database on recent-onset inflammatory joint disease and, more specifically, on RA to serve for scientific research in the clinical, epidemiological, pathophysiological, and healthcare-cost fields. Ten years after enrolment were started, the cohort still has about 500 patients. The scientific committee has approved 104 clinical research projects, of which many are ongoing, and 54 original articles written by numerous French and international groups have been published. These projects cover a vast spectrum of topics including environmental factors, diagnosis, outcomes, prognosis, disease evaluation, imaging, genetics, biomarkers, costs, and RA management strategies.