Concerning the critical function of teachers' teaching autonomy in instructional practice and professional development, this study explores the relative importance of three predictive mechanisms: a. professionalism of teachers, b. complexity of teaching practice, and c. culture of individualism. Using the sample of 118,347 teachers from 8262 schools in 27 countries derived from the 2018 Teaching and Learning International Survey (TALIS), we applied a three-level hierarchical linear model (HLM) for analysis. We found that teachers’ teaching autonomy was mainly predicted by the professionalism of teachers and the culture of individualism rather than the complexity of teaching practice. Implications for individual teachers, school leaders, and policymakers are discussed.