This report discusses how different strategic level institutional arrangements in the civil-military interface influence the operational conduct and effectiveness of armed forces involved in complex peace support operations. The report notes that there are at least two important civil-military aspects of effectiveness. The civil-military interface must function effectively as the provider of well trained and equipped forces of adequate size and nature for modern operations, which is referred to as the indirect impact of civil-military relations. The civil-military interface must also function effectively as an important level in the operational chain of command, providing co-ordinated ciivil-military analysis, planning and execution of operations. This direct impact of civil-military relations is the main focal point of the report. Without well functioning civil-military relations, effectiveness in complex peace operations is unlikely. In essence, for increased effectiveness, the civil-military interface should strive towards increased integration of the military and civilian echelons. The purpose of such integration is to create enough mutual trust, knowledge and understanding across the civil-military divide to provide both the necessary structures, and a working culture, that serve to co-ordinate the different instruments of power towards intended political effects in the field. The empirical cases of the study are US and British civil-military relations at the strategic level of command, and their respective conduct of operations in Iraq.