The Incident Command System emphasizes orderly and systematic planning and the Incident Action Plan is the central tool for planning during a response to an emergency. The Incident Action Plan is prepared with input from the appropriate sections and units of the Incident Management Team. It should be written at the outset of the response and revised continually throughout the response. 

Incidents vary in their kind, complexity, size, and requirements for detailed and written plans. In an initial response for an incident that is readily controlled, a written plan may not be necessary. Larger, more complex incidents as well as hazardous materials incidents require an Incident Action Plan to coordinate activities. The level of detail required in an Incident Action Plan will vary according to the size and complexity of the response.