During the mid-century wave of decolonization, the ecumenical movement sought to dissociate Christianity from its role – real and perceived – as a handmaiden of empire. At the same time, the WCC and IMC sought to anchor Christianity in the constitutions of postcolonial states, in order to secure the religious freedom of missionaries and Christian minorities, especially in majority-Muslim countries. Ecumenical advocacy thus sought to enshrine the international norm they had shaped in the Universal Declaration’s Article 18 in domestic law. After discussing the wider trajectory of the ecumenical movement in relation to empire, this chapter turns to two important cases: Indonesia and (Northern) Nigeria. In each case, the ecumenical movement successfully influenced the drafting of postcolonial constitutions, using the language of human rights to claim impartiality while enhancing Christianity’s position vis-à-vis Islam. In doing so, ecumenists drew on their ties to departing colonial powers, the influence of those missionaries and Christian minorities that remained, and postcolonial leaders’ desire to establish essentially secular states.