Introduction. In a rapidly changing world, traditional models of professional development that focus on knowledge and skill transfer are no longer effective in fostering flexible competencies and self-development. The study of the potential of formative professional development is a response to these challenges. The purpose of the study was to provide a scientific basis for understanding the essence, content, and practical implementation of formative professional development for educators. Materials and methods. The work used the ideas of a systemic and personality-oriented approach, the principles of acmeology and axiology in relation to the professional development of a teacher. The study was conducted through a structural and comparative analysis of the theoretical and methodological foundations of the process of a teacher's professional development. Results. The framework of the research of the concepts “development”, “formation”, “professional development” included in the concept “forming professional development of a teacher” is determined. It was established that the forming professional development involves a directed change of the teacher’s personality, reflected in the acquisition of a new form of professionalism under the influence of certain factors and conditions of professional activity and opening up new ways for professional self-realization and effective activity. The key characteristics of a teacher's professional development were revealed: the active role of the teacher, constant striving for self-improvement, the presence of feedback, the acceptance of a state of crisis and the development of “deficient” abilities. The ideas of formative assessment in relation to the teacher's formative professional development were substantiated. The main strategies for implementing the teacher's formative professional development (educational, expert-evaluative, managerial, reflexive, motivational, and accompanying) were described. Conclusion. The formative professional development of a teacher is a new tool for improving professional and pedagogical activities. The perspective of studying the formative nature of a teacher's professional development is to consider it as a process of meaningful change in a teacher's personality and a mechanism for integrating the results of critical reflection into value-based attitudes towards professional growth.