The findings are based off key informant interviews conducted by local research teams in early 2019 with local traders, boat operators, merchants, port authorities and local governments across the island provinces of Basilan, Sulu and Tawi-Tawi, as well as Zamboanga City. Exploring the historical movement of goods between the Southern Philippines and Sabah, Malaysia, the report documents the networks, ports and sea routes that make up this vital yet illegal cross-border trade. Drawing from over 60 interviews with local traders, boat operators, port authorities, and others, the report lifts the lid on the informal economy which sits at the crossroads between a changing political environment in Southern Mindanao and shifting trends of violence and conflict. The report documents bribery and rent seeking by local government agents, and the impact of violent extremism and banditry on local trade and livelihoods. The research findings are an important contribution to ongoing policy discussions around fiscal and infrastructure arrangements for the new Bangsamoro Autonomous Region in Muslim Mindanao, as well as efforts to formalise barter trade.