This is a multinational, multi-center, observational, prospective, longitudinal disease registry designed to collect data on participants with cold agglutinin disease (CAD) or cold agglutinin syndrome (CAS). Among them, a minimum of 30 patients with CAD treated with sutimlimab are expected to take part in the sutimlimab cohort study. Patients with CAD who have been enrolled in previous sutimlimab clinical trials (e.g., BIVV009-01/LTS16214 \[NCT02502903,CAD patients\], BIVV009-03/EFC16215 \[NCT03347396\], and BIVV009-04/EFC16216 \[NCT03347422\]) and who either completed or discontinued the corresponding clinical trial are eligible to participate in the registry.