Early Internet scholars proclaimed that the transnational nature of the Internet rendered it inherently unregulable by conventional governments. Instead, the Internet would be governed by customs and practices established by the end user community in a manner reminiscent of the lex mercatoria, which spontaneously emerged during medieval times to resolve international trade disputes independently and autonomously from national law. Subsequent events have revealed these claims to have been overly optimistic, as national governments have evinced both the inclination and the ability to exert influence, if not outright control, over the physical infrastructure, the domain name system, and the content flowing across the network. These failures have done little to lessen the allure of Internet self-governance. In particular, some scholars have suggested that more widespread use of open source software would increase the Internet’s ability to resist governmental control. This Essay explores whether more widespread use of open source software might provide the basis for the type of bottom-up ordering associated with the lex mercatoria. Perhaps unsurprisingly, a system of self-governance based on open source implicates the same questions of spontaneity, universality, and autonomy that surround the lex mercatoria.