Exercise CYGNUS was a command post exercise delivered by Public Health England on behalf of the Department of Health. This was part of the Public Health England funded programme directed by the Emergency Preparedness, Resilience and Response Partnership Group chaired by the Department of Health. The exercise was designed to assess the United Kingdom's preparedness and response to a pandemic influenza outbreak. It was aimed at responders in Local Resilience Forums, NHS England and Public Health England at local, regional and national level, the Department of Health and other government departments, the Health Departments of Scotland, Wales and Northern Ireland and NHS Wales. This report identifies lessons relevant to all of the participating organisations and is not restricted to lessons reflecting only the experience of health organisations. The lessons identified in the report are not therefore necessarily PHE's corporate position; they are evidenced on the information gathered during the exercise and interpreted in the context of the Emergency Response Department's experience and judgement. It is suggested that the lessons identified are reviewed by the appropriate organisations to assess if any further action is appropriate.