Influenza pandemics are unpredictable but recurring events that can have severe consequences on societies worldwide. This revised WHO guidance publication on pandemic influenza preparedness and response has been developed to guide WHO Member States and others responsible for public health and pandemic influenza preparedness activities at the national level. It is the product of expert opinion, derived from several international consultations which included examination of available information and modeling studies, input from public health experts on lessons learned from SARS and both animal and human influenza responses, and consolidation of recommendations in existing WHO guidance. These recommendations were subject to an extensive public review.This revision acknowledges that pandemic preparedness is centered around health sectors planning but must also be broader. WHO therefore advocates a "whole-of-society" approach to sustainable and ethical pandemic preparedness while focusing in more detail on the role of the health sector. The roles of WHO and national governments are outlined to create a better understanding of how health and non-health sectors, both public and private, all contribute to pandemic preparedness.