[영문]The main burden of the paper is to argue for enlarging both the concept and the coverage of social security, especially in developing countries, to address the twin problems of qqqquot;deficiencyqqqquot; and qqqquot;adversityqqqquot;. The two parts of this enlarged concept of social security are Basic Social Security (BSS) and Contingent Social Security (CSS). To strengthen the argument, lessons have been highlighted from the historical experience of Western countries, where the State played a leading role. Having argued for the extension of BSS, the paper also deals with the extension of CSS. This is best done through the informal economy, which employs a large majority of workers in developing countries. While the primacy of the State has been highlighted, the paper develops a typology of various social security models that could be used to study and understand the existing arrangements as well as the potentialities for extension