Is purpose a cause, consequence, correlate, or component of well-being? Sense of purpose can be understood as the extent to which one feels that they have personally meaningful goals and directions guiding them through life. Because models of well-being differ in how they conceptualize what it means to be psychologically well, purpose is treated differently across these frameworks. In this chapter, we begin by considering how purpose fits in various well-being theories, including philosophical schools of thought (Liking, Wanting, and Needing theories), contemporary theoretical and measurement models (e.g., subjective well-being, Value Fulfillment Theory, Ryff’s psychological well-being, self-determination theory, Positive emotion, Engagement, Relationships, Meaning, and Accomplishments, and other factors such as health (PERMA+)), and mechanistic models that seek the synthesize across multiple approaches (e.g., Engine Model of Well-Being, Eudaimonic Activity Model). We conclude by answering the question proposed in the title of this chapter, “Where does purpose belong in well-being theory?”, and by offering specific recommendations for purpose and well-being researchers.