Illegal Unreported and Unregulated (IUU) fishing is a global threat to sustainable fisheries and to the management and conservation of fisheries resources and marine biodiversity. As a tool to combat IUU fishing, the importance of enhanced port state control has increasingly gained ground throughout the last decennium. The growing reliance on port states to combat non-sustainable fishing practices stems to a great extent from the failure of flag states to effectively control fishing operations carried out by vessels flying their flag. Port State Measures (PSM) are requirements established or interventions undertaken by port states which a foreign fishing vessel must comply with or is subjected to as a condition for use of ports within the port state. National PSM would typically include requirements related to prior notification of port entry, use of designated ports, restrictions on port entry and landing/transhipment of fish, restrictions on supplies and services, documentation requirements and port inspections, as well as related measures, such as IUU vessel listing, trade-related measures and sanctions. Many of these measures have in recent years seen their inclusion and development in international instruments.