The importance of the present research arises from the value that has been given – at the national, European, and international level – to the work of the teacher and the necessity of his or her professional development but also in the research gap that exists in this field. The aim of the research was to clarify the views of school principals on factors influencing their professional development. A questionnaire was administered through the Google form. The data were analyzed using the SPSS v.25. To reply to the research questions, the non-parametric Kruskal-Wallis and the Pearson coefficient were used to assess the statistical significance of the data. The sample consisted of 100 primary school principals in Greece. The results of the study showed differences in attitudes towards professional development between heads of primary education institutions with different specializations. Participants with a specialization in math and computer sciences more often supported the idea that their professional development depends on their basic studies. Those who specialized in humanities, agreed on a higher level that their professional development depends on their first two years of education experience, participation in introductory training programs, participation in training programs organized by the state and on the school culture, and their transition to another school or position. The participants who followed a science field were more positive about their professional development depending on their participation in European mobility programs, the professional support they get from their colleagues, and the way the school leadership is practiced. There were differences in the understanding of the role of the educational institution in supporting the professional development of teachers depending on the professional experience of the participants: its importance was recognized by teachers who had less than five or more than thirty years of professional experience. It was found that the more positive was the attitude of the participants toward their own professional development, the wider range of needs for further training they expressed. Most often, such needs related to improving professional competence in such areas as classroom management, solving problems with complex student behavior and school discipline, counseling, and assessment of students.