The chapter examines key theories driving public service motivation research. After discussing the origins of public service motivation, the discussion in chapter 2 is broken into three broad categories: theories related to predisposition-opportunity theory, theories related to self-determination theory, and theories related to goal-setting theory. First, the discussion related to predisposition-opportunity theory aims to answer the question of why people contribute different levels of personal resources to organizations. Predisposition-opportunity theory is then compared to attraction-selection-attrition theory and person-fit theory, and empirical research is examined. Second, self-determination theory adds to the discussion by positing that resource contributions can be explained by psychological needs and motivations. Commonalities between self-determination theory and public service motivation are analyzed before empirical research on motivation-crowding theory is discussed. Third, goal theory contends that differences in motivation and performance can be explained by differences in goals. Chapter 2 concludes with a discussion of the use of mission valence as a proxy for goals.