This chapter presents a chronological analysis of the activities of UN agencies in Mexico, a country with an important indigenous population, in which the UN agenda in relation to indigenous peoples has been very active since the UN opened its first office in the country, in 1947. The chapter analyzes the UN’s multi-agency work in Mexico from the 1950s to the 1970s. It explores the practices that the UN implemented in Mexico as part of its promotion of multiculturalism, which gradually replaced the assimilationist model as the dominant approach of UN bodies toward “indigenous populations.” The chapter also explores that intergovernmental institutions are capable of influencing the power relations that exist between indigenous peoples and the State. It describes the evolution of the policies and norms that the UN has implemented in assimilationist model, since the beginning of its engagement with indigenous issues in the early 1950s.