The goal of this paper is to report on the background and the methods used in the ICF Core Set development for patients in the acute hospital and early post-acute rehabilitation facilities. ICF Core Sets are sets of categories out of the International Classification of Functioning, Disability and Health (ICF) which can serve as minimal standards for the assessment, communication and reporting of functioning and health for clinical studies, clinical encounters and multi-professional comprehensive assessment and management. The ICF Core Sets were developed in a formal decision-making and consensus process, integrating evidence gathered from preliminary studies and expert opinion. The Acute ICF Core Sets for patients with neurological, musculoskeletal and cardiopulmonary conditions are intended for use by physicians, nurses, therapists and other health professionals working in the acute hospital on medical, surgical or other units not specialised in rehabilitation. The Post-acute ICF Core Sets for geriatric patients and patients with neurological, musculoskeletal or cardiopulmonary conditions are intended for use by physicians, nurses, therapists and other health professionals involved in early post-acute rehabilitation. The Acute and Post-acute ICF Core Sets are first versions and need to be tested and validated in the patient and professional perspective and in different countries, regions, health care and provider settings.