What are the temporal effects of preliminary rulings: Do court decisions take effect from the moment of the judgment announcement, or do they have retroactive effect to the moment the norm analyzed by the CJEU came into force? The dissertation discusses this question. After a theoretical classification of the topic based on two national legal systems, the work focuses on the effects of preliminary rulings that go beyond the individual case. At its core, it analyzes and evaluates the temporal effects of judgments under Article 267 TFEU: it outlines the rule-exception system established by the CJEU for interpretative and invalidity decisions based on case law. It elaborates on the conditions under which the CJEU is willing to refrain from retroactive effect of its decisions and critiques these conditions. The work concludes with a discussion of possible developments.