Former literature reviews suggested that if (student) teachers learn together in their professional development activities, professional development is enhanced. In the present literature review, we explored a variety of peer teacher professional development activities, conceptually divided into coaching, collaborating, and assessing activities. Specifically, we examined which learning outcomes could be achieved through participating in such activities. By means of a metastudy approach, we additionally reviewed methods, data collection, and theories used in the included studies. Findings showed outcomes were achieved in terms of teacher knowledge, teacher skills, and student learning. At the same time, many studies had methodological weaknesses: many self-report and self-constructed instruments hardly based on theory were applied. Based on the findings, we urge for more rigorous studies that can move the field forward.Teacher professional development (TPD) is considered to be an important approach for the improvement of quality of education (Borko and Putnam 1995;Coe et al. 2014;Desimone 2009;Hattie 2009). Many studies have explored what characteristics make TPD effective and concluded that TPD should focus on developing subject matter knowledge as well as pedagogical content knowledge, hold active and inquiry-based activities, span over a larger time period, and that teachers should work together with their colleagues (Desimone 2009;Putnam and Borko 2000;Van Veen, Zwart, and Meirink 2012). Examples of TPD wherein teachers learn with their colleagues are peer coaching (Ackland 1991) and communities of practice (Lave and Wenger 1991;Wenger 1998). In this article, we call such activities peer teacher professional development (PTPD) activities, and we will report on a review study that focussed on the learning outcomes of (student) teachers as a result of participating in such activities.In this review study, a variety of PTPD activities are combined into a comprehensive overview. On a conceptual level and based on different functions of the activities (e.g. Little 1990) and group size, we distinguish three different types of PTPD activities: (a) coaching, wherein individuals support another individual, reciprocal or non-reciprocal, in achieving individual goals (e.g. peer coaching, peer feedback); (b) collaborating, wherein larger groups this is an open access article distributed under the terms of the creative commons attribution-noncommercial-noderivatives license (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.