Mastery goals are generally considered the most adaptive achievement goals. In 2 studies, we tested whether, in line with self-determination theory, participants' experiences of autonomy support and autonomy would affect the relations between mastery goals and psychological outcomes. In Study 1 (an experiment), 117 college students, randomly assigned to 3 groups (autonomy-supportive, autonomy-suppressive, neutral), adopted an intrapersonal-competence standard to improve graphic quality of handwriting. Results showed that mastery goals led to more positive emotional experiences when given in an autonomy-supportive context relative to the other two. Study 2 extended the research to natural settings and learners' motives among 7th and 8th graders (n = 839) responding to questionnaires about a specific class. Results revealed stronger relations of mastery goals with interest and enjoyment and with behavioral engagement when students perceived their level of choice (experience of autonomy) as high rather than low. We therefore propose that research on achievement goals should consider both the contexts and the motives accompanying the goals.