Book excerpt: "Among the most influential models in contemporary behavioral science, self-determination theory (SDT) offers a broad framework for understanding the factors that promote human motivation and psychological flourishing. In this authoritative work, SDT cofounders Richard M. Ryan and Edward L. Deci systematically review the theory's conceptual underpinnings, empirical evidence base, and practical applications across the lifespan. Ryan and Deci demonstrate that supporting people's basic needs for competence, relatedness, and autonomy is critically important for virtually all aspects of individual and societal functioning."--Jacket.