Bachelor Thesis from the year 2017 in the subject Business economics - Banking, Stock Exchanges, Insurance, Accounting, grade: 1.3, University of Münster, language: English, abstract: The existing research focuses on two channels how stock (mis-)pricing influences firm investment. On the one hand, the informational role of prices is examined. The general conclusion shared by many papers is as follows: managers learn from high prices that the aggregated opinion of investors sees promising investment opportunities. Hence, decision makers invest because they either learn from actual new information or they want to cater the investors and keep the stock prices high because of personal incentives. On the other hand, the financing role of equity is investigated. Many papers come to the same conclusion. Mispriced stocks are equal to misvalued eq-uity. Consequently, if stocks are overpriced the cost of financing through issuance of new shares declines. If the cost of financing declines, more in-vestment opportunities seem to be promising. Therefore, the firm's investment activity increases. Additionally, third parties and potential debt lenders like banks evaluate the firm based on the stock performance amongst other aspects. If the stock price is high banks are more likely to issue credit and reduce their demands concerning the terms of debt (e.g. decrease inter-est rate). This is particularly important for financially constrained firms which are only able to invest in new projects if they are able to raise capital on their own. By following the approach of Polk and Sapienza (2009, pp. 191-194), my thesis examines if the relation of firm investment to stock mispricing is influenced by market concentration. At first, I regress firm investment on mispricing, investment opportunities and cash flow proxies on my whole sample. Afterwards I build sub samples based on market concentration and conduct the same regression on those sub samples again. Thereby, my re-search adds the dimension of market competition to the existing research. The thesis is organized as follows. In section 2 I briefly sum up the status quo in terms of research on the relation between mispricing and investment behavior. I state and explain my hypotheses in my third chapter. Following the explanations, I describe the data and methodology further in section 4. After evaluating my empirical results and documenting my robustness tests in section 5, I present my conclusions in chapter 6.