The Department of Defense (DoD) faces unprecedented challenges as the Nation confronts balancing a strong military to confront threats with the realities of diminishing financial resources. That each warfighter is a critical resource was underscored the Special Operations principal tenet "humans are more important than hardware." These challenges have popularized the term "human performance optimization" (HPO), which became ingrained in DoD around 2005. This article is the first in a new series relating to HPO, and we define the term and concept of HPO, describe other phrases used (e.g., performance enhancement; performance sustainment, performance restoration; and human performance modification). Last, we introduce an integrated model for HPO.