Since the emergence of the concept of sustainable development, lawyers across the globe are trying to come to grips with its legal status and the potential legal consequences (See Bosselmann, Sustainability law. Ashgate Publishing, 2008; French, Sustainable development. In: Fitzmaurice M, Ong DM, Merkouris P(eds) The research handbook on international environmental law. Edward Elgar, 2010, and Barstow Magraw D. Hawke LD, Sustainable development. In: Bodansky D, Brunnéé J, Hey E (eds) Oxford handbook of international environmental law. Oxford University Press, 2007). Nowadays, the concept of sustainable development is represented in legally binding texts at international, European, and national levels. Taking EU law as an example, both the Treaty on the European Union (TEU) and the Treaty on the Functioning of the European Union (TFEU) refer to sustainable development in several articles. This clearly means that sustainable development is part of EU law. The real question, however, is whether this reference to sustainable development in binding law has any significant consequence for legal practice. Can, for instance, the Court of Justice of the European Union annul a decision of the European Commission should this decision be qualified as conflicting with sustainable development? Such a far-reaching and dramatic annulment is most unlikely under EU law, while the potential legal consequences of sustainable development will probably be more subtle. This chapter provides insight into the appearance of sustainable development in international and EU law and gives observations on its possible legal effects and the importance of national decision-making in view of sustainable development.