This is the fourth edition of the Ontario Health Plan for an Influenza Pandemic (OHPIP), which is designed to guide planning at both the provincial and local levels across Ontario. It describes how Ontario’s health care system will respond to an influenza pandemic. OHPIP sets out a comprehensive province-wide approach to health preparedness and response planning, and provides information to guide local pandemic planning groups. OHPIP endeavours to strike a balance between providing enough direction to ensure a consistent provincial health response to an influenza pandemic, and giving local jurisdictions the flexibility to respond to different scenarios that may arise during a pandemic.