The debate on the future of the public pension system –including the contributory, obligatory and pay-as-you-go systems– became almost twenty years ago the debate par excellence on the Welfare State in Spain, being at the same time an object of consensus and conflict between political and social forces. This is due to three fundamental reasons: firstly, because this debate condenses almost all the political problems as regards the future of social protection in Spain; secondly, because it is a permanent object and cornerstone in the negotiations between the government, the trade unions and company representatives; finally, it is one of the most important vectors involved in the structuring of Spanish public opinion which at present, however, largely supports the existence of a pay-as-you-go pension system.