No major incident is ever truly resolved without a postmortem. It’s a way to look back and review the incident in detail to determine exactly what went wrong, why it went wrong, and what can be done in the future to make sure it doesn’t happen again. To that end, we’d like to share how we here at PagerDuty conduct postmortems internally. It is our hope that others will use the documentation as a starting point to formalize their own processes. This guide to postmortems provides information on what to do after a major incident and shares PagerDuty’s follow-up and after-action review procedures.