This thesis deals with the construction of the principle “knew or should have known”, which was initiated by the jurisdiction of the ECJ with regard to carousel fraud or MTICFraud. This principle is analysed by means of national and international judicature on VAT fraud. Further the essential legal framework conditions and the interpretation of the
doctrine is explained. An important aspect is the bona fide rights protection for the bona fide entrepreneur. In addition to the description of the carousel fraud or MTIC-Fraud the resulting financial crimes and consequences based on the Austrian fiscal penal code are also discussed. The national and international court decisions contain a number of criteria that are relevant to the assessment of the taxpayers knowledge of fraud. The analysis and elaboration of these criteria should give the entrepreneur an aid to identify the fraud in a timely manner and to avoid unintentional integration into the fraud.