Qualities of effective teachers matter because teachers are the number one school-related factor that impacts on student achievement. Although researchers in the United States have studied frameworks for evaluating teacher effectiveness, these frameworks are not focused on teachers working in international schools. Thus, they may not reflect the importance of understanding both the context of working in intercultural settings and the skills that allow teachers to flourish in international schools. Using a systematic configurative synthesis review of 23 studies, this study identifies qualities of effective teachers working in international schools through a synthesis of the study findings. We identified four key attributes that are emphasized, if not unique, in international school effective teacher research: a focus on teacher collaboration and teacher leadership; cultural awareness and responsiveness from multi-national perspectives; and host country language acquisition. Overall, we find that a focus on what makes an effective international school teacher is lacking in the extant research, particularly given the predicted enormous growth of international schools.