The tax consequences of civil law transactions with economic substance are difficult to predict. One explanation is that tax legislation is constantly changing and under strong political pressure. The "normal" legal system is not able to deliver sufficient predictability, which is why the institution of "advance ruling" has been introduced. It is a form of tax process before a transaction is carried out or a tax return is filed. A taxpayer seeks an advance ruling before the Tax Tribunal. The Tax Agency is the other party before the Tribunal. The ruling given, which states how taxation should be carried out in the situation described, can be appealed by any party to the Supreme Administrative Court (HFD) without leave to appeal being granted. The characteristics of the institution are regulated by the short law on advance rulings and supplemented by administrative law. The procedural rules are sparsely codified and the case law of the Supreme Administrative Court is important for understanding the system. In recent years, debate has arisen about the purposes and functioning of the Institute. As a result of rulings by the Supreme Court, uncertainty has arisen about what can be the subject of the application. The primary aim of the project is to systematize and analyze the relevant legal sources in order to increase knowledge about the nature and meaning of the Institute. It also aims to determine the purpose and function of the Institute and whether there is a need for reform or the need for additional procedures.