Fuelled by the recent turn towards global history, a growing body of historians has started to describe European expansion in the nineteenth and twentieth century as a shared colonial project characterised by common basic assumptions, patterns of thought and techniques. But historians have hardly asked how interimperial commonalities came into being. Besides referring to transimperial processes of transfer, which led to the harmonisation of patterns of thought and practices, some historians have pointed to the possibility of a common reservoir of knowledge that all imperial powers could access. How such an “imperial cloud” might have emerged and functioned is the topic of this special issue.