The purpose of this paper is to explore the notions of teachers' professionalism and professional development by investigating the views of in-service primary teachers in Greece. An empirical study was carried out at the In-Service Teachers' Training School of the Department of Primary Education of the University of Patras, Greece. Our research data were collected by using anonymously filled in questionnaires. The results revealed that the teachers of our sample were acquainted with the issues of professionalism and sought to enhance their professional development. They also stressed the importance to be offered more opportunities for lifelong learning education. This study expands our understanding of the factors which affect teachers' professionalism and professional development.