In complex, humanitarian emergencies, professional liaison roles are just one of many that evolve from the coordination of United Nations agencies, the International Committee of the Red Cross, international and national non-governmental relief organizations, and coalition military forces. Liaison is crucial to the humanitarian relief process. Decision makers benefit from liaisons' professional experience, their knowledge of the characteristics, missions, and capabilities of each major participant in the relief process, and in their ability to coordinate and clarify professional issues in meeting the goals of a mission. Medical liaison roles develop from the awareness that complex emergencies primarily are catastrophic public-health emergencies. Unfortunately, education and training of the medical liaison currently are ill-defined. However, limited experience suggests that skills should be broadly based in principles of disaster epidemiology, assessment and management, knowledge of contributing relief resources, agencies and the military, and international humanitarian law and the Geneva Conventions.