When UNESCO was founded in 1945 the organization aimed to become a pivotal player in international collaboration in the field of engineering. UNESCO based its engineering initiatives on the World Engineering Conference, an organization espousing a politically motivated “technocratic internationalism” and on the World Power Conference, an organization promoting a business-friendly stance of “engineering internationalism.” These competing models for international collaboration curtailed UNESCO’s institutional ambitions. UNESCO’s position was further weakened by fierce opposition from British engineering institutions that pursued a Commonwealth institutional framework in direct opposition to UNESCO. This article unravels the intricate connections between empire and internationalism that shaped UNESCO’s engineering agenda during the first post-war decades. It demonstrates how competing forms of internationalism, mounting cold war tensions, and the continuous influence of a British empire-based opposition ultimately forced UNESCO to abandon its technocratic internationalist ambitions and settle for a modest coordinating role in international technical collaboration.