Human Systems Integration (HSI) is a robust process by which to design and develop systems that effectively and affordably integrate human capabilities and limitations. It includes humans, in their different roles in the system (as operator, maintainer, trainer, designer, etc.). Systems including hardware, software, and processes (including the acquisition process and the design process), and the integration of all of these elements to optimize the performance and safety of the whole. HSI should be included as an integral part of a total system approach to weapon systems development and acquisition.
The Defense Acquisition Guidebook (DAG) states, “The total system includes not only the prime mission equipment, but also the people who operate, maintain, and support the system; the training and training devices; and operational and support infrastructure”.
Guidebook: Air Force Human System Integration Handbook
Human Systems Integration (HSI) Goal
The principle goal of HSI is to ensure a safe and effective relationship between the human and the system that meets the mission.
Benefits if Human Systems Integration (HSI)
There are a few benefits for HSI that are listed in the DAG to include 
- Provide a better operational solution to the warfighters.
- Lead to the development or improvement of all human interfaces.
- Achieve required effectiveness of human performance during system testing, operation, maintenance, support, transport, demilitarization and disposal.
- Ensure the demands upon personnel resources, skills, training and costs are planned and accounted for at every stage in the system life cycle.
- Ensure that overall human performance is within the knowledge, skills and abilities of the designated operators, maintainers and users to support mission tasking.
Human Systems Integration (HSI) Topics
HSI is a multidisciplinary field of study composed of several basic areas: [1,2]
- Human Factors Engineering
- Integrated and comprehensive analysis
- Design and assessment of requirements
- Concepts and resources for system manpower
- System Safety
- Health Hazards
- Personnel Survivability
Human Systems Integration (HSI) Concepts
There are three (3) key concepts that define an effective HSI program. 
- Systems are comprised of hardware, software, and human personnel all of which operate within a surrounding environment. Too often, acquisition systems programs fail to consider the human capacity or requirements as part of the system. This leads to poor task allocation between hardware, software, and human users or supporters. To promote ideal task allocation, it is critical that the human element be considered early in system development.
- Successful HSI depends upon the integration of the functional HSI domains into acquisition planning efforts such as participation on program High-Performance Teams (HPTs) and Integrated Product Teams (IPTs).
- HSI must be considered early in the requirements development phase of system design and acquisition. This will provide the best opportunity to maximize return on investment (ROI) and system performance. HSI requirements must be developed in conjunction with capability-based requirements generation through functional analyses within the Joint Capabilities Integration and Development System (JCIDS). HSI requirements will drive HSI metrics and embed HSI issues within the system design. After a system is designed, implementation of HSI oversights can be very expensive.
Human Systems Integration (HSI) in the Acquisition Process
HSI should also be addressed in the following acquisition-related documents.
- Systems Engineering Plan (SEP)
- Test and Evaluation Master Plan (TEMP)
- Software Development Plan (SDP)
- Life-Cycle Sustainment Plan (LCSP)
- Other appropriate program documentation
AcqLinks and References:
-  Air Force Human System Integration Handbook
-  Defense Acquisition Guidebook (DAG) Chapter 5
- HSI and ESOH Handbook for Pre MS A JCIDS and AoA Activities – Oct 13
- Website: Naval Post Graduate School – Human System Integration
- Website: MIL-HDBK-759B: Human Factors Engineering Design for Army Materiel
- Website: Air Force Human Systems Integration Office