This paper reports the findings of an investigation into English as a foreign language (EFL) teachers’ self-efficacy and their classroom management in the context of the Mekong Delta of Vietnam. The paper also aims to find out what makes teachers different in terms of skills in classroom management. The study was designed as a descriptive mixed-methods one, using a questionnaire, focus group interviews, and classroom observations to collect data. Forty-six EFL teachers from three high schools responded to the questionnaire. Twelve got involved in the semi-structured interviews, and six as classroom observed teachers. Two group interviews were conducted with the participation of three vice-principals and three heads of English teams. The results indicated a significant interaction between EFL teachers’ self-efficacy and their classroom management skills. Teachers who own a higher level of self-efficacy showed to manage their classes in a more confident and purposive manner than those with a lower level of self-efficacy. Three main reasons differentiating teachers’ skills in classroom management, including pre-service teacher education, previous attending continuing professional development events, and teacher’s learning autonomy were detected. Case-based teaching, organizational learning, and lesson study are recommended in pre-service teacher education and in-service teacher professional development activities to enhance teachers’ self-efficacy and their classroom management.