Even a casual observer of human behavior can see that there are profound differences in how individuals regulate their actions. Some individuals doggedly pursue a single goal or ideal for many years, making many personal sacrifices and at great personal cost. Others seem to give in to their immediate impulses with barely a thought for the consequences. Some students earn their highest grades under severe stress and in the face of adversity. The same levels of stress and adversity may lead other students to drop out and abandon their academic goals altogether. Indeed, many students seem to perform best under more relaxed conditions. At the workplace, some employees demonstrate high levels of initiative and set their own agenda, regardless of what others may think. Others prefer to follow the instructions of their superiors, and are eager to learn what is expected of them.

These and other individual differences in self-regulation are the central focus of the present chapter. The following sections offer some preliminary reflections on the neglect of individual differences in psychological research. Next, the chapter considers individual differences in motives and needs, and how global notions of self-regulation and the will can be decomposed into more specific psychological functions and mechanisms. Finally, this chapter shows how this functional analysis of the will can be used to understand a wide array of effects of individual differences in affect regulation (i.e., action vs. state orientation).