The purpose of this thesis is to shed light on the importance of preparation and specialised knowledge for interpreters working for the ECJ. For this purpose, a general insight is given into interpreting at the ECJ, which has barely been discussed so far in professional literature. Subsequently, the thesis deals with the preparation and the specialised legal knowledge of interpreters as well as the reciprocity between these two elements. The theoretical foundation for the study comprises an overview of the working environment, thus the ECJ, and highlights relevant questions with respect to interpreting studies. The empiric study consists of five semi-structured interviews with permanent and freelance interpreters working for the ECJ. In order to gain general insight into the field of interpreting for the ECJ, the compiled data served as expert knowledge to describe the day-to-day work of the interpreters. Thereafter, the elements ?preparation? and ?legal knowledge? were analyzed following the Grounded theory method. The study showed that the interpreters act systematically when preparing a hearing and it allowed to identify Individual and collective strategies of preparation. It therefore corroborates the results from prior studies that emphasize the importance of preparation. All of the interpreters possess legal knowledge, which they acquired either formally or practically and extend constantly by working for the ECJ. The interpreters interviewed shared the opinion that specialised knowledge is far less important than preparation. Furthermore, the study revealed that topical preparation as one important element of the individual strategies of preparation is tantamount to the practical acquisition of legal knowledge. On the contrary, legal knowledge could be detected as being an intervening condition, which affects the strategies of preparation particularly with regard to their extent and content.