To be eligible to receive payment from Medicare, hospitals must be certified to meet certain conditions. Hospitals may gain such credentials by choosing to be reviewed by a state certification agency under contract to the Centers for Medicare & Medicaid Services or to be accredited by either the Joint Commission on Accreditation of Healthcare Organizations or the American Osteopathic Association. This issue brief looks at how accreditation of hospitals developed and how it continues to change. It considers the legal and practical reasons that a majority of hospitals choose accreditation and why some hospitals do not, along with broader consideration of the extent to which accreditation may be judged of value to Medicare beneficiaries. The intersection of state and federal oversight responsibilities and the role of accrediting organizations in hospital quality improvement also are examined.