Self-determination theory is a broad and widely applied theory of motivation, personality development, and wellness. The theory began with a narrow focus on intrinsic motivation but has expanded over time to encompass both intrinsic and extrinsic motivations and spawned new perspectives on well-being, life-goals, relationship quality, vitality and depletion, and eudaimonia, among other topics. In this overview of SDT, we first discuss the value of broad theory for psychological science. We then describe the strategy behind SDT's development, and the unfolding of its core mini-theories and topical models, from early studies on intrinsic motivation to the enormous body of research being produced today by a global community of SDT scholars. Throughout we highlight evidence for the critical role of supports for autonomy, competence and relatedness in human development and thriving, and the strong practical and translational value of a functionally-focused, and empirically-supported, theoretical framework.