The purpose of this volume is to seek out, describe, and explain the shared commonalities of stress, fatigue, and workload. To understand and predict human performance response, we have to reach beyond the sterile, information-processing models to incorporate the emotive, affective, or more generally, energetic aspects of cognition. These facets of behavior surface most readily when the individual acts under stress, is faced by significant cognitive workload, or is in the grip of fatigue. However, energetic characteristics are pervasive and exert a vital and ubiquitous influence, even when they are not obviously in play as in extreme circumstances. Indeed, one cannot hope to understand behavior without their inclusion and integration into models and theories. This text addresses such theoretical questions as one of its main thrusts. However, in addition to the drive for scientific understanding, there are requirements in our progressively more utilitarian society which generate the need for a more fundamental understanding of this particular topic.