People are centrally concerned with motivation -- how to move themselves or others to act. Everywhere, parents, teachers, coaches, and managers struggle with how to motivate those that they mentor, and individuals struggle to find energy, mobilize effort and persist at the tasks of life and work. People are often moved by external factors such as reward systems, grades, evaluations, or the opinions they fear others might have of them. Yet just as frequently, people are motivated from within, by interests, curiosity, care or abiding values. These intrinsic motivations are not necessarily externally rewarded or supported, but nonetheless they can sustain passions, creativity, and sustained efforts. The interplay between the extrinsic forces acting on persons and the intrinsic motives and needs inherent in human nature is the territory of Self-Determination Theory.