After the War, it seemed impossible to restore relations between France and Germany. However,their relationship was asked to be modified by new situations. Cold war was one of the most importantchallenges to the United States and European countries which had to agree on rebuild of the economy ofEurope. The United States decided to put into effect Marshall Plan, a large-scale financial aid, since 1948,and requested to European partners creation of organizations to support it and the collective guarantee to avoidanother war. As such, CEEC to support the plan, and Council of Europe and NATO for European collectivesecurity were created. Until then, relationship between Germany, excluded from these movements, and Francewas far from being improved. It was in 1950 that dramatic reconciliation was achieved at the moment of thecreation of ECSC. This paper aims to analyze the improvement of old enemies’ relationship through theoriesof international politics: theory of national interest and institutional theory. First, France and Germany hopedto strengthen national interests through reconciliation. Allowing Germany to join European and internationalcommunities, France was able to secure coal and steel, and collective control over old enemy. Germany couldstart to get out of the shadow of defeated country, joining as a normal one international organizations and gettingeconomic and political cooperations from neighbor countries. Second, their reconciliation was institutionalizedand stabilized by new institutions, such as ECSC, EEC and Eurotom, and by becoming a member of Councilof Europe and NATO. Their reconciliation contributed to development of European integration.