Horioka's findings have become known as the “Feldstein-Horioka Puzzle”. Social security, induced retirement and aggregate capital accumulation Published in 1974, this article made a significant contribution to social insurance. Feldstein facilitated a greater understanding of the effects of social security upon household consumption and savings. The article provides a theoretical analysis of the impact of social security on an individual’s decision regarding retirement and the amount of savings necessary for such retirement. Feldstein revealed that Social Security results in individuals deciding to save less for retirement and to retire earlier. The finding was later contested because it contained a calculation error. Feldstein and other authors did not agree on whether the corrected results made a change of the conclusions necessary. The European Union, the euro and the sovereign debt crisis Martin Feldstein participated in the academic and popular debate on the European Union (EU) and the European common currency from its early stages, with increased interest during the sovereign debt crisis. Taking a political economy perspective, Feldstein argued that the European Union project in general and the creation of the Economic and Monetary Union (EMU) in particular were driven by a strange mix of pro-European internationalism and the pursuit of strictly national interests. Although nuanced in his criticism, Feldstein can be characterized as a Eurosceptic. Feldstein, an enthusiastic supporter of a single market for goods and services in the EU, argued that this goal does not require a monetary union. Furthermore, the creation of a single currency in the EU would increase political tensions in the union, as not all countries share the anti-inflationary stance of the German policy makers. In military and foreign policy, the objective of achieving a political union (of which the monetary unification is only one aspect) would promote the development of a common foreign and defense policy capable of projecting strength on the international scene. During the sovereign debt crisis, Feldstein argued in favor of a "eurozone holiday" solution whereby the countries most affected by the crisis (such as Greece) would temporarily leave the eurozone, revert to their national currencies, devalue and re-enter at a lower exchange rate a few years later, a policy that would ensure a boost in international competitiveness solid enough to offset the economic recession. Teaching A well-known figure on the Harvard campus, Feldstein taught the introductory economics class "Social Analysis 10: Principles of Economics" for 20 years and was succeeded