In this book comparative analysis is given of the way governments and social security systems reacted to the challenges facing established social security systems - and also social security systems to be established - in the context of the end of the XXth century: globalization and the changes it has brought in the perception and possibilities of establishing or maintaining the welfare state. The selection of countries is due to both scientific criteria - it has been decided to start with western industrialized countries - and non scientific ones: the availability of specialists in selected countries. It is clear therefore that, even if restricted to western industrialized countries, the sample of countries which are studied here are not representative of all the main systems of social security. Countries such as Germany, France and the Netherlands are clearly missing for those readers who are looking for a broad description of existing systems. Looking at the different chapters of this book, a rather diverse and broad overview of problems and solutions are given, adapting social security systems to the environment of the XXIst century.