executive summary: This essay identifies trends and actors involved in illegal, unreported, and unregulated (IUU) fishing in two of Southeast Asia's regional seascapes (the South China Sea and the Sulu-Sulawesi Seascape), explores the political and socioeconomic factors that enable IUU fishing, and offers recommendations to governments and other stakeholders. main argument IUU fishing threatens the food, ecological, and economic security of coastal communities in Southeast Asia's seascapes. The region is home to incredible marine biodiversity that supports commercially important fish stocks. However, IUU fishing, poor fisheries management, and bad governance—coupled with environmental degradation and a lack of monitoring, control, surveillance, and enforcement capacity—leave these stocks in a precarious position. The clandestine nature of IUU fishing can also attract crimes of convergence, including forced labor and trafficking of humans, arms, drugs, and wildlife. To counter IUU fishing, national governments in Southeast Asia should take steps to improve cooperation, build cohesiveness, and share data and relevant information with each other and with regional organizations. Likewise, the Association of Southeast Asian Nations and regional fisheries management organizations should take a greater leadership role to facilitate data and information sharing between Southeast Asian governments. policy implications • Cooperative and joint stock assessments in the South China Sea and the Sulu-Sulawesi Seascape by governments, scientists, NGOs, and other stakeholders, with a focus on transboundary stocks, would significantly improve the monitoring and management of fisheries. • To bridge gaps in enforcement capacity, fisheries enforcement authorities should work with nontraditional partners, including local communities and trusted nations in the Indo-Pacific, such as the U.S., Australia, Japan, and the Republic of Korea. • Southeast Asian coastal states should work together to settle remaining maritime boundary disputes they have with each other and develop a cohesive regional bloc that strengthens their collective commitment to the UN Convention on the Law of the Sea and efforts to combat IUU fishing. • National governments and law enforcement should increase their capacity and technical capabilities to stop labor and human rights abuses on the water and in seafood processing facilities by working with NGOs, survivors, and other relevant stakeholders with expertise in the field.