Abstract : This report documents a strategic planning methodology, Assumption- Based Planning, the RAND has developed over the last four years. It distills long-range planning work for the Training and Doctrine Command (TRADOC) Research Activity and the Manpower, Training, and Performance Program (now the Manpower and Training Program) of RAND's Arroyo Center and was funded as Arroyo Center exploratory research. This work was conducted to aid the U.S. Army with its long- and mid-range planning. As argued, the method is particularly suited to planning in the military. It should also be of interest to anyone engaged in long-range or strategic planning. This report is intended to describe the fundamentals of Assumption-Based Planning and to provide numerous examples, although it is not a complete user's manual