In the second half of the nineteenth century, geologists created the International Geological Congress (IGC) to achieve the methodological and terminological uniformity that they thought their science lacked. Their desire to standardize their practice and their use of the conference to do so was neither new nor unique. Although late nineteenth-century international conferences have been recognized as important arenas of standardization, relatively little is known of the ways in which conferences organized standardization negotiations. This article aims to fill this gap (...) by exploring how the IGC practically and socially organized standardization work. It appears that the session hall was not the sole and not even the main stage of geological standard-setting. The standardization process was also enacted through comparative study and informal exchanges that regular visits to purpose-built comparative geological exhibitions made possible. Relying on a sophisticated apparatus of commissions and subcommittees, the IGC also socially organized standards negotiation beyond the space and time of the triennial sessions. By tracing the material, spatial and social practices engineered through the IGC to serve geological standardization, this article unboxes the conference process and in so doing enriches our understanding of the period's wave of standardization. (shrink)