The aim of the present thesis is to investigate cognitive biases, which describe systematic malfunctions in the human decision-making process, as well as their causes and consequences in business activities. Thus, scientific findings in psychology and social sciences are analysed with a particular focus on their impact on the role of managerial accounting. Biases may affect the processing of relevant information, therefore three examples are introduced: framing, mood congruency und anchoring bias. Due to the fact that even qualified decision makers are likely to fail, e.g. when under time pressure, the topic provides an opportunity for improving the selection and presentation of information to the management. Biases also influence risk attitude and competitive behaviour, which are explained introducing three major topics: optimism and overconfidence in managerial decision-making, escalation of commitment concerning failing projects, and competitive irrationality. As a result, the relevance of biases and their potentially threatening consequences become obvious. There is a variety of alternative countermeasures presented in the literature. The majority aims at reducing biases and their effects by creating awareness, using financial incentives or organisational and technological tools. Concerning the presented biases, those methods yield only mixed results. In some scenarios, it is neither possible nor preferable to eliminate biases. Sometimes a minor deviation from rational behaviour might even provide better results. In those cases, managerial accounting should modify either incentives or the contextual framework in order to induce decisions, which support the objectives of the company.