The article dwells on professional development of public school teachers as an inevitable constituent of education systems in the 21st century. In such economically developed countries as Great Britain, Canada and the USA, the problem of preparing teachers to a difficult and responsible task of upbringing and educating future citizens always remains topical. The authors define the following aim and objectives of their research: to conduct analysis of scientific and pedagogical literature and to define the notion of teachers' "professional development"; to research a place and role of the constructivist approach to professional development of teachers. Some aspects of the problem under research have been studied by foreign and domestic scientists: political, social, cultural and economic aspects of teachers' professional development (L. Darling-Hammond, M. Tight); elaboration of professional development curricula (C. Pratt); content of teachers' professional development (N. Dana Fichtman, S. Zepeda); concept-oriented instruction (J. Guthrie); continuing professional development (Ya. Belmaz, A. Kuzminskyi, O. Kuznietsova). The research methodology comprises theoretical (logical, structural and systematic methods, induction and deduction, comparison and compatibility, analysis and synthesis) and applied (observations, questioning and interviewing) methods. The research results have been presented.