Vygotsky's sociocultural theory of human learning describes learning as a social process and the origination of human intelligence in society or culture in which the social and cultural context of development cannot be separated. The sociocultural theory of mind attempts to explain the processes through which learning and development occur. A tenet of Vygotsky's sociocultural theory is the zone of proximal development (ZPD), which is used as a measure of the distance between what a learner is able to do and a proximal level that they might attain through guidance and collaboration with a more knowledgeable other. The ZPD is important in both education and psychology. By understanding how ZPD and a teacher's ZPD (TZPD) function, teachers and professional development (PD) trainers can be better prepared to create meaningful learning opportunities which maximize the tools and strategies available to educators, thus further improving student learning outcomes. The absence of current research on TZPD, especially in regard to reading comprehension instruction, results in the lack of evidence for how teachers develop TZPD and use evidence-based reading comprehension strategies in classroom instruction. The goal of this study was to investigate previous research conducted regarding Vygotsky's Zone of Proximal Development and its implications for preservice and in-service teachers through what has been termed teachers' zone of proximal development. A systematic literature search identified studies tied to ZPD and TZPD. After screening and elimination, 13 studies were selected and reviewed for study design, theoretical framework, constructs being investigated, and the impact of methods used to collect data related to ZPD and TZPD.