Disponible también en formato electrónico.

Resumen.

Assessment of the time at which newly introduced or amended legislation takes effect is difficult. This is due to the possibility that some legal rules apply to situations existing before their entry into force. These rules are in principle retroactively applicable. The European Court of Justice evaluates retroactivity of (tax) legislation based on a distinction between procedural and substantive rules. Procedural rules are held to apply to proceedings pending at the time when they enter into force. Substantive rules are usually interpreted as not applying to situations existing before their entry into force. However, retroactive effect must be given to these rules in so far as it follows clearly from their terms, objectives or general scheme. This is to ensure observance of the principle of legal certainty and the protection of legitimate expectations. Violation of these principles is only allowed on legitimate grounds. This article compiles a framework constituting the general principles of Union law and Article 1 First Protocol European Court of Human Rights. This framework can be used to assess whether legal provisions are applicable before their entry into force. The framework is tested with a case study to the retroactive effect of Title III UCC provisions.