Legal ignorance typically refers to a situation where one is ignorant of the existence of a certain legal prescript or is ignorant of the precise understanding of a prescript or its consequences. In Belgian law, there is no general provision dealing with legal ignorance or its consequences with effects. In principle, one cannot escape the application of law based on the mere fact that one does not know the law or its consequences. However, in specific situations Belgian law and case law deviate from this basic principle, provided that strict conditions are fulfilled. The authors of this article report on the application of the concept of legal ignorance in the areas of contract law, tort law and prescription. As for contract law, the article examines whether a mistake as to the law may qualify as an excusable error leading to the nullification of a contract. Although the Cour de Cassation applies a very strict interpretation and states that mere legal ignorance cannot be an excusable error, some lower courts seem to apply a more lenient interpretation. In tort law, the starting point remains that mere legal ignorance is not excusable. To escape liability despite the infringement of a specific rule, one will have to overcome the difficult task of proving that the mistake was ‘unavoidable’. Lastly, the general provision for prescription periods does not deal explicitly with the issue of legal ignorance. In principle it is not necessary that the person subject to prescription is aware of the fact that the prescription started to run. In specific situations, some statues and case law deviate from this principle.