This paper examines the rise of various forms of patent expertise over the course of the second industrialisation. The essential insight here is that patent agents and lawyers, as well as consultant engineers, became, in the late 19th century, critical actors in the production and transmission of patent rights and patented technologies within and among societies. This paper considers three main themes. First, the global institutionalisation of patent agents during the late nineteenth century and their growing centrality in several national systems. Second, the transnational patenting networks created during the 1880s, particularly the activities of associations of patent agents and their impact on the making of an international patent system. Third, the controversial role of patent experts as agents of corporate globalism. The most important point remains that agents’ powers, and their many services to multinational corporations, had enduring consequences on the structure of knowledge property worldwide.