Most Asian populations are undergoing population ageing, but the degree of ageing varies considerably. This paper examines the patterns of population ageing in the countries of Asia since 1950. It finds six geographically-defined groups, within which ageing patterns are relatively homogeneous. The underlying causes of population ageing are demographic transition, involving the decline of both fertility and mortality, and international out-migration. Rapid economic development and demographic transition are associated with advanced ageing. In contrast, warfare and significant unrest, and low levels of development are associated with delayed demographic transition and reverse ageing. The consequences of population ageing can be formulated as two main social security challenges: income support in retirement and the provision of personal care. The viability of traditional support systems has been brought into question in the context of increased longevity, small family size, changed gender relations, the out-migration of children for employment and the demands of the modern economy. In fact, the intergenerational contract is being upheld through a series of adaptations including diversified living arrangements, monetary transfers and gifts, attitudinal change, revised expectations and a relaxation of customary roles. These adaptations often do not adversely affect the well-being of elders. The establishment of formal old-age social security systems in Asia has been slow relative to other countries. System reform is beginning to meet the challenges of fiscal sustainability posed by ongoing population ageing. Social pensions (safety nets) are more commonplace; though their value remains low, social pensions are instrumental in reducing poverty and increasing well-being in old age. Policies that support adaptation through state social security systems and other enabling measures will enhance the well-being of the older and working generations alike.