This article suggests the relevance of diffusionism in discussing the past, the present, and the future of the International Relations (IR) norm diffusion literature. The paper argues, thus, that IR norm research has reproduced the diffusionist and beyond-diffusionist mechanisms and epistemologies that the anthropological research on culture diffusion has developed, and this has been consequential for the discipline. Accordingly, the diffusionism dominant in the mainstream IR norm research has led to the normalisation of normative hierarchies and power asymmetries between geographies in the diffusion context. The critical norm research, complementarily, while extensively criticising such biased scholarly practices, failed to diagnose the problem as diffusionism and thus failed to benefit from the informed conclusions the anthropological schools offered regarding beyond-diffusionism in diffusion research. The paper takes this as a basis for highlighting the necessity to further extend the dialogue between IR and social sciences and humanities on issues including diffusion.