The Social Security system, universally acknowledged to be one of the most key political issues of the 20th century, is experiencing growing pains. This study, which analyzes the public and private old age pensions schemes in Spain, aims to determine the precise dimension of the reform that must be carried out: for reasons of constitutional imperative; the social and economic requirements of our time; and the innate dynamic nature that social protection systems have. The study constitutes a contribution to the research Pensiones y prestaciones por desempleo (Pensions and Unemployment Benefits) (Fundación BBV, page 66).