Before you can even begin to answer that question, you need to know that ergonomics and usability are just two major parts of a much broader picture. (As shown to the right)
Even among practitioners & researchers there is modest disagreement on what work falls under which domain.
This site is intended to inform potential students of ergonomics, HCI, or usability; employers seeking to know more about ergonomists & usability professionals and whether they should hire one (see Goals) and to anyone who wants a quick reference to major organizations and certifications (see Qualifications & Community)
For the purpose of this website, and based on the interviews of several high profile ergonomists, the term human factors will refer to both usability experts and ergonomists; usability professional refers to both usability and to a certain extent HCI (human computer interface), and ergonomics refers strictly to the physical work of human factors. See defintions for a better understanding or visit any of the major websites listed under Community.