The relationship between theory and discipline is problematic for human factors and ergonomics (HFE). We address the following constituent issues: (a) the present state of theory usage in HFE; (b) the reasons underlying this state; (c) the need for theory in HFE; (d) what HFE professionals (including educators, journal editors, and individual researchers) should do to encourage the proper use of theory; and, (e) the outlines of a metatheory of HFE. A metatheory is a general framework that may help professionals to construct more useful specific theories. Our metatheory of HFE involves five basic units, or classes of variables: task, environment, personnel, tool, and performance. Each unit in turn has multiple components (i.e., specific variables). Use of the metatheory is illustrated with specific examples. Our hope is that researchers will be motivated to make explicit and useful connections between their research and necessary theory, to the improvement of both; the metatheory may be useful in this endeavor.