Studying the co-operation between the Economic Commission for Europe (ECE) and the Council for Mutual Economic Assistance (COMECON) allows understanding to what extent the shaping of statistical development indicators constitutes a Cold War challenge. These indicators contributed to the scientific legitimation of antagonistic socio-political systems. Between the mid 1960s and the mid 1980s, the ECE and the COMECON were very active in elaborating a new statistical knowledge about social development, as well as in organising the comparability of existing economic statistics. This engagement in the new field of social indicators was part of a strategy promoting their institutional autonomy and political legitimacy in the long term, vis-à-vis both their Member States and competing international organisations. The failed coordination of their co-operation agendas prevented the adoption of social indicators as the main development indicators on the international stage. However, their collaboration contributed to the shaping of a panEuropean network of statistical experts, which kept the Eastern Bloc part of the scientific exchanges that took place during the Cold War.