Hugo Grotius was a widely read and influential figure in seventeenth-century England. Whereas later generations portrayed him as a forefather to modern theories of natural and international law, the publication of Mare Liberum (1609) offered a grounded argument for free trade against the restrictions imposed by the Spanish and Portuguese colonial empires. But Grotius's notion of free trade, of course, was far removed from the later ideal of Richard Cobden. His model of commercial organization was firmly anchored on the chartered mercantile company, and he served as a spokesperson for the Dutch East India Company (VOC) during the Anglo-Dutch Conferences of 1613 and 1615, which sought to appease growing tensions among Dutch and English trading interests in Asia. As the diplomatic and economic relations between England and the Dutch Republic progressively deteriorated during the early decades of the seventeenth century, Grotius's rendition of the law of nations came increasingly to be regarded as a rationalization of Dutch dominance over long-distance trade routes. English commentators, who wished to emulate Dutch success but feared aggression and subordination, had to fashion a different framework of international politics to sustain their vision of an emerging English maritime empire. Tracing the uses of Mare Liberum in the mercantile literature of early Stuart England, the paper will study how this foundational work of modern international thought shaped the political economic discourse of English merchants, as well as their supporters and adversaries in the political arena. Changing attitudes toward Grotius's arguments will help us identify the origins of certain ideas about empire that later came to the fore by the time of the Navigation Acts and the Anglo-Dutch wars. We will thus explore how Grotius's version of the law of nations -- before it was retrospectively converted into a cornerstone of liberal internationalism -- was entangled in concrete disputes between rival imperial projects.