Reference materials are an important requisite for ensuring reliable laboratory measurements and thus appropriate patient care. To ensure that a reference material is suitable for its intended purpose, its characteristics need to be assessed in a defined manner, taking all relevant aspects into consideration. This document provides information to help material manufacturers in the production and characterization of commutable reference materials as well as assist assay manufacturers, proficiency testing providers, and laboratorians in the appropriate use of these materials for calibration and trueness assessment of in vitro diagnostic medical devices. Guidance on qualification requirements of reference materials related to the definition of the measurand, the intended use of the material, and other material specifications is provided. Information on study designs, data evaluation, and uncertainty assessment is included that is supplemental to existing guidance documents about the assessment of homogeneity, stability, and property values. This document provides a revised definition of the term 'commutability' and provides guidance on how to perform commutability evaluation.