Lessons learned is a structured review conducted after security incidents, crises, or exercises. The goal is to determine what worked well, where process weaknesses existed, and what specific improvements should be implemented. ISO 27001 requires continual improvement (clause 10.1), and lessons learned are a central mechanism for this. Conduct the review promptly while memories are fresh and involve all participants. The findings feed back into your ISMS as corrective actions. Document insights in a way that remains accessible to future teams.