Ergonomics, also known as Human Factors or Human Factors Engineering (HFE), is the scientific discipline concerned with the understanding of interactions among humans and other elements of a system, and the profession that applies theory, principles, data, and methods to design in order to optimize human well-being and overall system performance. It involves the application of psychological and physiological principles within the domains of engineering and design, encompassing products, processes, and systems. The primary goals of human factors engineering are to reduce human error, increase productivity and overall system performance, and enhance safety, health and comfort. A specific focus of this field is the interaction between the human and other sociotechnical elements.

The field applies theories, principles and data from a variety of primary or pure disciplines, such as psychology, sociology, engineering, biomechanics, industrial design, physiology, sociotechnical systems, human-computer interaction, anthropometry, interaction design, visual design, user experience, and user interface design. Human factors research employs methods and approaches from these and other knowledge disciplines to study human behavior and generate data relevant to human-system interface technology to achieve previously stated goals. In studying and sharing learning on the design of equipment, devices, and processes that fit the human body and its cognitive abilities, the two terms, "human factors" and "ergonomics", are essentially synonymous as to their referent and meaning in current literature.

As defined by the International Ergonomics Association, the principal domains of specialization include: Physical ergonomics, which is concerned with human anatomical, anthropometric, physiological and biomechanical characteristics as they relate to physical activity.  (Relevant topics include working postures, materials handling, repetitive movements, work related musculoskeletal disorders, workplace layout, safety and health.), Cognitive ergonomics, which is concerned with mental processes, such as perception, memory, reasoning, and motor response, as they affect interactions among humans and other elements of a system.  (Relevant topics include mental workload, decision-making, skilled performance, human-computer interaction, human reliability, work stress and training as these may relate to human-system design.), and Organizational ergonomics is concerned with the optimization of sociotechnical systems, including their organizational structures, policies, and processes. (Relevant topics include communication, crew resource management, work design, design of working times, teamwork, participatory design, community ergonomics, cooperative work, new work paradigms, virtual organizations, telework, and quality management.)

Human factors engineering (HFE) is relevant in the design of such things as safe furniture and easy-to-use interfaces to machines and equipment. Proper ergonomic design is necessary to prevent repetitive strain injuries and other musculoskeletal disorders, which can develop over time and can lead to long-term disability. Human factors and ergonomics are concerned with the "fit" between the user, equipment, and environment or "fitting a job to a person" or "fitting the task to the man". It accounts for the user's capabilities and limitations in seeking to ensure that tasks, functions, information, and the environment suit that user.

To assess the fit between a person and the technology being used, human factors specialists or ergonomists consider the job (activity) being performed and the demands on the user; the equipment used (its size, shape, and how appropriate it is for the task); and the information used (how it is presented, accessed, and modified). Ergonomics draws on many disciplines in its study of humans and their environments, including anthropometry, biomechanics, mechanical engineering, industrial engineering, industrial design, information design, kinesiology, physiology, cognitive psychology, industrial and organizational psychology, and space psychology.