Increasing attention is being directed to the competency of those who deliver healthcare in the United States. In behavioral health, there is growing recognition of the need to define, teach, and assess essential competencies. Since attention to this issue in behavioral health is relatively recent, there is much to be gained by learning from the principles, definitions, and conceptual models of competency that have been developed in other fields. This article outlines the forces that drive the current focus on competency of the healthcare workforce. Relevant history, principles, definitions, and models that have evolved through research and application in business and industry are reviewed. From this analysis, recommendations are offered to guide future work on competencies in behavioral health.