AbstractReviews the book edited by W. F. Floyd and A. T. Welford . This report of both English and American workers is concerned with various aspects of inadequate performance of the human, and techniques for detecting and measuring them. Both old and new slants are represented. While the symposium is labeled as one on fatigue, no verbalized convention is agreed upon as to what is fatigue and what is to be otherwise defined. Welford explicitly recognizes that there are several distinctly different phenomena called fatigue. One is a subjective state related to some kind of physical or mental strain. The other is a decrement in performance following more or less prolonged activity. Nowhere throughout the printed report of the symposium does there seem to be a recognition that the topic of fatigue is in an undefined and therefore unusable state for intelligent discussion and inquiry. There was no recognition of the logically intolerable condition of having a number of terms used synonymously in technical discourse; e.g., fatigue, boredom, tiredness, work decrement, disorganization of performance, and impairment. Because of this deficiency and what follows from it, all these very careful and ingenious studies lack the orientation and meaningfulness that they would otherwise have. To close with a positive note, it can be said that the reader will find in the symposium a number of ingenious experiments that are well worth their acquaintance.