Illegal, unreported, and unregulated (IUU) fishing remains one of the greatest threats to marine ecosystems due to its potent ability to undermine national and regional efforts to manage fisheries sustainably as well as endeavours to conserve marine biodiversity. IUU fishing takes advantage of corrupt administrations and exploits weak management regimes, in particular those of developing countries lacking the capacity and resources for effective monitoring, control, and surveillance (MCS). IUU fishing is found in all types and dimensions of fisheries; it occurs both on the high seas and in areas within national jurisdiction, it concerns all aspects and stages of the capture and utilisation of fish, and it may sometimes be associated with organized crime. Fisheries resources available to bona fide fishers are removed by IUU fishing, which can lead to the collapse of local fisheries, with small-scale fisheries in developing countries proving particularly vulnerable. Products derived from IUU fishing can find their way into overseas trade markets thus throttling local food supply. IUU fishing therefore threatens livelihoods, exacerbates poverty, and augments food insecurity.