In recent years, the financial service industry demonstrated substantial growth of Exchange Traded Funds (ETFs). Apart from offering access to new and more specific investment opportunities, many ETFs enter direct competition with conventional, already existing Mutual Index Funds. With 22,1% growth of assets over the past 5 years, the European market by now accounts for 19% of the global ETF market, while at the same time we observe a decline of cash flows to Mutual Index Funds. Given the recent development, index investors are likely to face a choice between ETFs and Mutual Index Funds offering the same service. The purpose of this study is to analyze those two similar investment instruments towards the quality of achieving their objective, which is to deliver a performance as close as possible to the respective benchmarks'. The analysis will be performed for the European market, i.e. we include only Index Funds that track European indices. This study is guided by objectivism and positivism as ontological and epistemological positions. We conduct a deductive research by reviewing and testing previous findings through the formulation of hypotheses that serve our purpose. For our analysis we gather quantitative data in the form of daily prices for 21 ETFs and 22 Mutual Index Funds, tracking 9 European indices. We further use a time frame of 7 years (2006-2012), which we analyze as a whole as well as divided into sub-periods as determined by different states of the European market. As a basis for the analysis we calculate return differences and different measures of tracking risk. Our results show that on average ETFs as well as Mutual Index Funds sufficiently replicate index performance with approximately the same level of tracking risk for both instruments. Furthermore, we see no significant impact of expected returns or index volatility on return difference. However, through examination of fees and tracking errors during recent economic turmoils, we show that ETFs first bear lower directly attributed costs and second are less affected by down markets than Mutual Funds.