The International Classification of Functioning, Disability and Health (ICF) is a key tool for rheumatology to assess and manage patients with chronic diseases. It provides a comprehensive framework for understanding the impact of disease on body functions, activities, and participation in society. The ICF was developed by the World Health Organization (WHO) and is part of the Family of International Classifications. It aims to improve the integration of health information and is used in clinical practice, research, and healthcare organization. The ICF includes 1,454 descriptions of functioning, divided into categories for body functions and structures, activities, participation, and environmental/personal factors. ICF Core Sets are being developed for specific conditions and healthcare situations, allowing for targeted assessment of functioning. These Core Sets are currently being tested and validated, with the first versions published for 12 chronic conditions, including musculoskeletal diseases. The ICF offers a universal framework for functioning, moving beyond the traditional impairment–disability–handicap model. It incorporates the bio-psychosocial model, considering environmental and personal factors. This framework aligns with the WHO's definition of health, including physical, mental, and social well-being. The ICF is used to measure functioning through qualifiers that indicate the extent of impairment or the role of environmental factors. While the ICF is not intended to replace existing instruments, it provides a standardized approach for assessing functioning. Researchers and clinicians can use the ICF to design studies, evaluate interventions, and improve patient care. The ICF is also valuable for healthcare organizations and governments, as it supports disability assessments, eligibility for technical aids, and social service organization. It helps in planning social security systems and home care, and in assessing disability pensions. Despite its strengths, the ICF faces challenges, including the need to develop classifications for personal factors and the Generic Core Set. There is also a need to improve the feasibility and understanding of the ICF among a wider audience. Future efforts will focus on refining the ICF to better meet the needs of patients, healthcare providers, and policymakers. The ICF is a critical tool for improving the understanding and management of functioning in patients with chronic diseases.The International Classification of Functioning, Disability and Health (ICF) is a key tool for rheumatology to assess and manage patients with chronic diseases. It provides a comprehensive framework for understanding the impact of disease on body functions, activities, and participation in society. The ICF was developed by the World Health Organization (WHO) and is part of the Family of International Classifications. It aims to improve the integration of health information and is used in clinical practice, research, and healthcare organization. The ICF includes 1,454 descriptions of functioning, divided into categories for body functions and structures, activities, participation, and environmental/personal factors. ICF Core Sets are being developed for specific conditions and healthcare situations, allowing for targeted assessment of functioning. These Core Sets are currently being tested and validated, with the first versions published for 12 chronic conditions, including musculoskeletal diseases. The ICF offers a universal framework for functioning, moving beyond the traditional impairment–disability–handicap model. It incorporates the bio-psychosocial model, considering environmental and personal factors. This framework aligns with the WHO's definition of health, including physical, mental, and social well-being. The ICF is used to measure functioning through qualifiers that indicate the extent of impairment or the role of environmental factors. While the ICF is not intended to replace existing instruments, it provides a standardized approach for assessing functioning. Researchers and clinicians can use the ICF to design studies, evaluate interventions, and improve patient care. The ICF is also valuable for healthcare organizations and governments, as it supports disability assessments, eligibility for technical aids, and social service organization. It helps in planning social security systems and home care, and in assessing disability pensions. Despite its strengths, the ICF faces challenges, including the need to develop classifications for personal factors and the Generic Core Set. There is also a need to improve the feasibility and understanding of the ICF among a wider audience. Future efforts will focus on refining the ICF to better meet the needs of patients, healthcare providers, and policymakers. The ICF is a critical tool for improving the understanding and management of functioning in patients with chronic diseases.