In this chapter, Massimo Lando focuses on the advisory jurisdiction of international courts and tribunals. This chapter explains that, traditionally, advisory opinions are not seen as a means of inter-State dispute settlement. However, it argues that recent developments justify re-assessing this traditional view. This chapter claims that the most significant development in this context is the judgment on preliminary objections delivered by the Special Chamber of the International Tribunal for the Law of the Sea in the maritime dispute between Mauritius and Maldives, which gave binding effect to the determinations made by the International Court of Justice in its 2019 advisory opinion concerning the decolonisation of Chagos. This chapter evaluates the Special Chamber’s decision by considering its impact on the Eastern Carelia doctrine and the Monetary Gold principle, as well as its implications for the legal effects of advisory opinions and for the legitimacy of exercising the advisory function.