In this chapter, the authors summarize self-determination theory and consider evidence related to this theory that highlights people’s ability to act autonomously in accord with integrated values, and to be mindful of, and able to resist, habitual ways of acting. The authors also summarize a large body of findings showing that with a sense of autonomy, people are more successful at attaining both personal and collective goals, more prosocial and connected to others, less defensive, and more vital and alive. Of course, the authors do not deny that autonomy is challenged by outside and internal forces (a key issue in classical existential philosophy), but the limitations of a deterministic perspective become clearer when one focuses on human capacities for self-awareness, choice, and integrity. This chapter in particular shows how a far-reaching scientific approach to existential concerns can support, rather than challenge, a humanistic sense of freedom and autonomy.(PsycInfo Database Record (c) 2023 APA, all rights reserved)