This chapter discusses the way the European Union promoted three types of consistency (institutional, vertical and horizontal) in a different way over the periods 1956-1977 and 1978-1991 in its relations with the International Labour Organization (ILO). During these two successive periods, the type of consistency sought changed as a result of the evolution of the acquis communautaire, and of the extent to which this body of Community law was (a) relevant to the agenda items of the ILO and (b) regarded as more technically sophisticated than the ILO standard-settings, or not. The chapter draws on archival documents from the European Commission, European Parliament, European Court of Justice, Economic and Social Committee and the International Labour Organization, as well as on secondary literature. Its purpose is to provide a historical foundation to the more developed literature that has emerged in the 2000s and that studies EU-ILO relations since the late 1990s. It shows that institutional consistency was the first dimension of consistency looked for by the EU, followed by vertical and institutional consistency. As a result, after 1991 all three dimensions of consistency are considered to be important. By providing for a long-term chronological account, we show that it is the breadth of the acquis communautaire that provides the best explanation for changes in types of consistency.