The International Classification of Functioning, Disability, and Health (ICF) created by the World Health Organization provides both a framework and a classification comprehensively covering domains of function and disability in rheumatologic patients. The ICF can be used as a universal language understood by medical doctors, health professionals, researchers, patients, and other groups. It is based on an integrative biopsychosocial model of functioning. For its implementation in rheumatology and medicine in general, practical ICF-based tools such as the ICF Core Sets are necessary. These Sets, which were developed in a standardized scientific process, consist of the ICF categories that are most relevant for a specific group of patients, e.g. chronic patients with rheumatoid arthritis. In rheumatologic rehabilitation, patient problems, medical findings, treatment goals, and treatment concepts can be structured by applying the ICF, ICF Core Sets, and an ICF assessment sheet to patients. In outcomes research, ICF Core Sets can support the selection of relevant outcome domains.