This book describes how demographic developments influence the Canadian Social Security System, not only through the evolution of the size and age structure of the Canadian population, but also through the possible economic consequences of a decreasing and ageing population. The second chapter will situate the reader in the historical context of social security systems in the world, it also provides and overview of the Canadian Social Security System. The third chapter analyzes the whole system in tercos of the systems approach and the demographic accounting. The fourth chapter describes the models that have been developed and that provide a structure for the connection of all the variables involved. The fifth chapter shows the results derived from the application of the models. Finally, the sixth chapter will delineate the main conclusions reached through the models' results and their analysis, as well as possible alternative uses for the model presented.