Why are some students more engaged in and adjusted to school than others? Why are some students more competent and why do they perform better than others? Self-determination theory is a theory of human motivation to explain students’ classroom behavior, learning process, and relationship with the environment. The goal of this paper is to review the concept of autonomy support in the classroom within the self-determination framework. Autonomy is defined as a form of voluntary action, stemming from a person’s interest and with no external pressure. Social environments that support autonomy provide meaningful rationale, acknowledge negative feelings, use noncontrolling language, offer meaningful choices, and nurture internal motivational resources. In classrooms where teachers support autonomy, students improve their academic performance, are more creative and better adjusted, engage more in school, and feel less stress. We provide theoretical and methodological suggestions for future research.