Social security is the protection provided by a given society to individuals and households, particularly in the case of old age. The design and scope of social security protection differs significantly across geographical regions, countries, and population groups, while also undergoing constant transformation over time. On a global scale, the area of social security witnessed three major paradigm shifts over the past 125 years: (1) formalization, sparked by Bismarck’s social insurance legislation in the 1880s; (2) privatization, initiated in the 1980s in Latin America and subsequently spreading to other regions, mainly Eastern Europe; and (3) universalization, as exemplified by the proliferation of non-contributory benefits in the Global South since the 2000s. This chapter outlines these trends to illustrate the transformation of social security in both the Global North and the Global South.