This Guide discusses the uses of certified reference materials (CRMs) and their correct applications. Clause 2 of this Guide presents definitions (with indication of their sources) of terms used, and clause 4 sets out the statistical considerations on which the Guide is based. Clause 5 discusses the role of CRMs in measurement science and in realization of conventional measurement scales. Clause 6 presents recommendations for developing criteria for the assessment of the precision and trueness of a measurement procedure by the use of CRMs. It pertains only to CRMs characterized to be homogeneous as described in ISO Guide 35 [4].