My dissertation explores the contractual dynamics of merchant networks in the 19th- and early 20th-century Western Indian Ocean, looking at the formal and informal rules that tied the members of these networks together and how these interacted with one another in the context of competing and overlapping legal jurisdictions. The commercial rules that prevailed in this ocean basin did not simply constrain the transacting partners, but generated enough trust between them to sustain regular patterns of commerce over great distances and long periods of time. I examine the relations of debt that characterized both production and commerce, binding together members of merchant network in a series of reciprocal rights and obligations. Using merchant correspondence and large caches of court cases, my goal is to reconstruct the ways that a cosmopolitan but largely Islamic business culture coped with the expansion of the British Empire and how the debt relations that underpinned commercial society in the Indian Ocean also contributed to this imperial expansion. At a more abstract level, my project explores the juncture at which informal institutions of contractual enforcement interact with dynamic formal institutions to establish economic order over time and space and throughout political change.