In order to insure that ISO 14001 is audited consistently across the world, the International Standards Organization (ISO) has created ISO 66, a standard that accreditation bodies use to assess registrars with. However, there are international differences in interpretation of this standard, particularly between the United States and Europe. This paper highlights these differences and their implications to registrar practices and organizational environmental performance. A careful analysis of the requirements by the International Accreditation Forum (IAF) Guidance to ISO 66, the Dutch council for Accreditation (RvA), and the American National Standards Institute-Registrar Accreditation Body (ANSI-RAB) uncovered significant differences in registrar requirements. It is concluded that these differences may be responsible for the variability found in registrar practices. Which, in turn, may have influenced the level of environmental performance characteristics exhibited by their ISO 14001 certified companies. Broad differences in accreditation requirements ultimately leads to a loss of credibility for the ISO 14001 certification, thus losing a potentially effective tool for encouraging volunteer efforts towards environmental responsibility and sustainability.