The concept that planning in advance for major emergency incidents is an important and valuable activity is seldom questioned. While most emergency response agencies engage in pre-incident planning to some extent and have established a level of cooperation and coordination with other agencies, there is no common denominator for the extent to which those efforts are applied. Experience with actual incidents almost invariably indicates the strengths or weaknesses of those efforts, after a major incident occurs. Interagency cooperation and coordination may be the most essential factor for handling unanticipated situations effectively. In this paper the Federal Emergency Management Agency (FEMA) reviews a series of effectively managed major local emergencies that represent a broad spectrum of circumstances. This review of the factors that contributed to their successful management clearly demonstrates the value of planned interagency relationships, particularly among neighboring jurisdictions, between agencies, and between levels of government.