This chapter explores the functions of various emotions for social units of varying sizes. D. Keltner and J. Haidt posit three types of social units: the individual, the dyad, and the group. For each unit, emotion functions in one of three distinct ways: a basic survival function, a communication function, and a social coordination function. P. Salovey and J. D. Mayer introduced the concept of emotional intelligence, a capacity to pay attention to and understand one's own emotions and those of others, and subsequently to use those emotions to guide behavior and decisions. B. L. Fredrickson proposed the broaden-and-build theory, which describes the ways in which the positive emotions such as joy, interest, and contentment help an individual respond to opportunities to thrive. The physiology of emotions and the motivating component of emotions themselves appear to help individuals respond adaptively to environmental threats and opportunities.