For further information, visit www.audiciaux.fr, www.scobex-rgpd-dpo.fr and www.dpo-externe-rgpd-france.fr. This guide details ISO 17021, a key standard for the certification of management systems. It explains the principles of impartiality, competence and transparency, as well as the certification process: audits, management of non-conformities and follow-up. Illustrated with concrete examples, it helps auditors and certification bodies to guarantee reliable and compliant assessments.