The "poverty of theories" of social security has long been at issue in Japan. However, in view of the structural changes that are occurring as a result of the rapid aging of the country's population, there is a need to undertake a fundamental examination of the present and future direction of social security in order to address the specific problems before us, including long-term care for our senior citizens. This paper reviews the history of socioeconomic changes caused by industrialization and aging and compares systems for providing social security here and abroad. The present situation in Japan is considered from the viewpoint of the "convergence of social insurance and social welfare (public assistance)." Based on this analysis, ideal ways of constructing a social security system for the future are contemplated.