This article investigates the growth of cross-border movement and migration in the northern portion of the Yellow Sea during the sixteenth century, which generated ongoing interactions and tensions with the coastal governance of Chosŏn Korea and Ming China. The fluid flow of private seafarers reconnected the northern Yellow Sea and revitalised its maritime economy, making this space an integral part of wider trade networks. Meanwhile, the Chosŏn and Ming authorities also attempted to discern, categorise, and institutionalise this transmarine mobility in their discursive, administrative, and geographic spaces. Instead of considering the two polities as land based and inward looking, this article foregrounds the dynamics of their coastal control mechanisms, while at the same time paying close attention to their constraints on filtering and scrutinising maritime violence.