Retroactivity in criminal adjudication: The flexibility-foreseeability dilemma

In balancing flexibility with foreseeability in criminal adjudication, two fundamental state duties (security and freedom) collide.
At first glance, the legality principle in criminal law requires maximum foreseeability but, also in order to optimize inter alia deterrence, effective criminal law and justice requires flexibility in the application of law. Domestic and international courts have to deal with this tension.
Separation of powers and the role of the judiciary are at the heart of the debate on adjudicative retroactivity. In this context, two techniques have been deployed to face the flexibility-foreseeability dilemma: prospective overruling and mistake of law.
This presentation questions how various courts within Europe, paying also attention to the European Court of Human Rights, view and manage the flexibility-foreseeability dilemma in the context of judicial retroactivity.