Organisations frequently carry out audits to evaluate their occupational health and safety performance. This book examines the application of regulation UNE-EN-ISO 19011 to occupational health and safety management systems based on OHSAS 18001. The purpose of the work is to offer guidance on doing internal audits, not forgetting its use in external audits, plus the competence and evaluation of the auditors and the performance of the auditees in the auditing process. In order to facilitate understanding and application of the regulation, the guide includes practical examples of specific situations, such as the documentation produced in the auditing process.