The author describes an approach to the analysis of emotion that can be used independently of conventional emotion theories: that expression, feeling, and motivation can be considered in a scientific manner. As a central theme he argues that biological and, in particular, evolutionary considerations are useful in understanding the basic components of emotion, and he applies this idea to a wide variety of the phenomena of emotion. The resultant review should be useful as an undergraduate text in which the explanations are aimed at the nonspecialist. The specific conclusions should be of interest to anyone who conducts research on emotion, and particularly those who need a solid framework on which to base interdisciplinary studies.