This document is, within the Human Resources Domain (HUM), one of the human factors modules dealing with human performance. This module suggests that human factors should be integrated throughout the Air Traffic Management (ATM) system life-cycle in order to reduce cost and make ATM systems safer and more effective. The module will provide the reader with an awareness of the benefits from integrating human factors into the ATM system life cycle and the cost associated herewith. The module will accommodate an understanding of the effects of both taking specific human factors initiatives and the way in which cost develops over the life-time of the system.