The text deals with the importance of theory and pedagogical practice in teacher’s professional development. It shows the specifics of professional development and the role of the teacher’s individual effort to learn at every stage of his development. The paper exposes the relationship that arises between theory and pedagogical practice, and emphasises the need for performing activities that are different then previous activities, due to a new social and educational situation. Recognizing these relationships leads to the emergence of pedagogical theory as the intellectual basis for the teacher’s practice and practice as the source of theoretical pedagogical knowledge and the place where theoretical constructs are verified. An important element of the analysis is the importance of pedagogical knowledge and practice achieved in various roles: teachers as researchers, reflective practitioners and professionals. Finally, the paper emphasises the need for flexibility of the teacher’s work, his ability to reflect on it, its effects and context, and understanding of these activities and of inspiration to create a vision of change. Those skills are regarded as important determinants of professional development.