The organizational backbone of the post-First World War international order was the League of Nations and the bureaucratic backbone of the League of Nations was its permanent Secretariat. The Secretariat was a radically novel invention in international politics. For the first time a permanent, autonomous international body had been created that managed international affairs and was populated with a multinational staff loyal only to that body. This chapter explores how the Secretariat managed to establish and develop this role for itself. It does so through two analytical steps. First, it explores the early, principled decisions regarding the Secretariat’s organization taken by its first Secretary-General, British diplomat Sir Eric Drummond, to ensure the Secretariat became a genuinely international body with substantial institutional autonomy. Second, it maps what we may, with a conceptual loan from Caterina Carta, term the metadiplomatic activities of the Secretariat, i.e. the activities carried out by the Secretariat leadership in order to develop close and productive relations to its main stakeholders: member states, other League institutions and international public opinion with the overall aim of establishing and expanding its legitimacy