After-action review is a professional discussion of an event, such as a disaster exercise, conducted during or immediately after each event. It focuses on performance standards and enables participants to discover for themselves what happened, why it happened, and how to sustain strengths and improve weaknesses. After-action review can be classified into formal after-action review and informal after-action review. A formal after-action review is resource-intensive and involves the planning, coordination, and preparation of supporting training aids, the after-action review site, and support personnel. While informal after-action review requires less preparation and planning.