The article reveals the essence of the definitions «lifelong education», «lifelong professional education», «system of lifelong education». An urgent problem today is to search ways to modernize and improve the system of lifelong professional education in order to make education meet the needs of society as a whole and each individual in particular at each level. The variability of surrounding reality is the basis for change in society and social institutions. Lifelong professional education cannot exist in isolation from other social systems. Education is the engine for the development of society (economic, political, social, etc.). The interpretation of the concept of «lifelong education» by different authors is analyzed, various contexts are considered (as a concept, as an aspect of educational practice, as a principle of educational organization, as a principle of state policy implementation, as modern trend, as a paradigm of scientific and pedagogical thinking). The roles of lifelong education (for an individual, for society, for the state, for the world community) are considered. Developmental stages of lifelong education (V. Onushkina, O. Tonkonoga, T. Desyatova, N. Nychkalo) are investigated. The problems of modern professional education are considered (subject education, elemental approach, separation of the subjects of the educational process from its results, the absence of quality requirements at each stage, etc.) and suggested ways to eliminate them. The characteristics of lifelong learning (duration, motivation, goals and objectives, network of educational services) are analyzed. The functions of lifelong professional education are considered: socio-cultural (developmental), general education (compensatory), adaptive and economic. The priority directions of lifelong professional education development are analyzed: intellectualization of education; personality-oriented approach; educational services market; modernization of all types of support; social partnership; international cooperation. The requirements for lifelong professional education at present stage of society development are formulated and characterized. The system of lifelong professional education is considered as a dynamic system that is in constant development.