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Germany represents a particular case in Europe because of the occurrence of two major structural changes since the end of the Seventies: first the reunification of the Federal Republic of Germany and the German Democratic Republic in 1990; then the implementation of the Euro currency in January 1999. This paper endogenously dates and tests for the presence of one or several structural breaks in the joint dynamic process of GDP and the unemployment rate. Following the methodology initiated by Blanchard and Quah [1989], it identifies the respective contributions of aggregate supply and demand shocks, prior to the estimated break and after it. This empirical study, based on post-1979 data, reveals: a significant break at the end of the year 1997, which corresponds to the implementation of the Stability and Growth Pact. the predominance of the supply component in the fluctuation of output for the period immediately preceding the Euro implementation; subsequently to the break, this predominance remains verified in the short run for the unemployment rate and in the medium run for output. Classification JEL: C32, C5, E32.