A major nonconformity is an audit finding that indicates a significant failure to meet a standard’s requirements. This could mean an entire required process is missing, or an existing process is systematically failing to achieve its intended purpose. In ISO 27001 certification audits, a major nonconformity blocks certificate issuance until you demonstrate effective correction. Certification bodies typically allow 90 days for remediation. You should perform a root cause analysis and document both the immediate correction and the corrective action to prevent recurrence.