DoD policy has introduced Human Systems Integration (HSI) terminology into the Human Factors Engineering (HFE) community. DoD 5000.2-R, Mandatory Procedures for Major Defense Acquisition Programs (MDAPs) and Major Automated Information System (MAIS) Acquisition Programs, requires a "comprehensive management and technical strategy for human systems integration..." be implemented for major acquisition programs. While the policy introduced the term, the process to implement HSI is often confused with human factors engineering. Human Systems Integration is the integration of seven distinct elements (Manpower, Personnel, Training, Human Factors, Safety, Health Hazards, and Survivability) within the system requirements and development process to achieve enhanced combat capability and reduced life cycle cost (LCC). These human elements were brought together to focus on the human's impact on the entire system's effectiveness and affordability. Incorporation of HSI design constraints and parameters in the development of a system ensures that humans are integrated into the system instead of accommodated after the system is designed. Human Systems Integration starts early in the requirements definition phase to identify human constraints and parameters and continues through to validation. Human factors engineering is the mechanism for implementing HSI into system design. Within HFE, trade-off analyses are conducted to balance the human constraints and parameters with the other system design constraints. This paper presents the US Air Force definition of HSI and the process we use to insure the integration of the human into our weapon system designs.