"In our introduction to this Special Issue of JESP, we first sketch what we know and what we do not know about the adaptation process to a society with a large proportion of older individuals. We develop a framework of empirical analysis which exploits the power of multidisciplinary, longitudinal and cross-national comparative data collection. Second, we provide a brief overview of SHARE, the Survey of Health, Ageing and Retirement in Europe. The 2004-05 baseline wave and the first longitudinal wave of SHARE collected in 2006-07 provide data on the life circumstances of some 45,000 individuals aged 50 and over in 14 European countries. SHARE constitutes a unique data infrastructure for researchers from various disciplines - notably economics, sociology and health - to better understand the individual and population ageing process. Third, we introduce the five studies in this Special Issue to show that the multidisciplinary, longitudinal and cross-national comparative data of SHARE permit a much better understanding of ageing and retirement in Europe than was possible before."

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