The purpose of this Master’s thesis is to analyse the role of the Food and Agriculture Organization of the United Nations (FAO) and the role of the European Union (EU) in fighting illegal, unreported and unregulated (IUU) fishing through Port State Measures (PSM). It is of great interest in terms of both international environmental law and international law of the sea to do research on IUU fishing because it is a global threat to sustainable fisheries and to the management and conservation of fisheries resources and marine biodiversity. The value and objective of this Master’s thesis will be to provide answers to four main questions. Firstly, “Are port State measures the most effective policies for national and international authorities to combat IUU fishing activities?”. Secondly, “Is the PSM Agreement sufficiently clear and precise to prevent, deter and eliminate IUU fishing?”. Furthermore, “Is the European Council Regulation on IUU Fishing consistent with existing international instruments and measures to combat IUU fishing?”. Finally, “Are the market-related measures set out in the IUU Regulation compatible with World Trade Organization (WTO) agreements?”. Master [120] en droit, Université catholique de Louvain, 2017