Key competencies had been defined as critical competencies, necessary competencies and important competencies. Several international organizations such as the United Nations Educational, Scientific and Cultural Organization (UNESCO), European Union (EU), Organization for Economic Co-operation and Development (OECD) all emphasized the importance of key competencies in educational reform. In this paper, the author argued the importance of key competencies from perspectives of individual development and social development, and articulated the function of key competencies regarding the notions of a successful life and a well-functioning society.