This thesis analyzes the monetary policy conducted by the European Central Bank (ECB) since 1999 from a theoretical, practical and empirical point of view, with special consideration of the euro crisis. For this purpose, the development and underlying problems of the crisis, as well as theoretical aspects of monetary policy topics are addressed. Furthermore, information about the ECB's monetary policy in theory and in practice provides the required knowledge for the interpretation of the econometric analysis. Conducting a single monetary policy for a diverse economic area has proven to be a major challenge, since the European Monetary Union does not constitute an optimal currency area. This led to tensions between the core and periphery countries. Non-standard monetary policy measures had to be undertaken by the ECB in order to achieve financial stabilization and reach its primary objective of price stability. A standard vector autoregression (VAR) model and a time-varying VAR model are used to perform an empirical analysis of the ECB's monetary policy. Focus lies on the development of the monetary transmission mechanism since 1999. The results strongly suggest a structural change in 2008 due to the onset of the financial crisis, which consequently entails a change in the transmission mechanism. Another breakpoint is suspected in 2012, possibly after the announcement of the Outright Monetary Transactions (OMT) program, which had a successful effect on market expectations and thus marked a turning point during the euro crisis. Mixed empirical findings on the functioning of the transmission mechanism after 2008 suggest strong negative reactions of economic variables to an interest rate shock during that period.