It seems a travesty to reiterate exactly what we mean by ‘Mesopotamia’. The tautological qualities of Greek mésos (‘middle’, ‘in between’) and potamós (‘stream’, ‘river’) often rule out further elaboration of its origins and the assumed self-evident nature of its current application. Yet regional concepts are not stable. Their delineation may be defined according to a complex set of attributes not related to physical borders alone. I consider here the changing meanings of ‘Mesopotamia’ as a name for the drainage of the Euphrates and Tigris from the 2nd millennium BCE until the present day. In conclusion, I argue that current notions of ‘Mesopotamia’ are a product of the First World War, and hence far from unproblematic references to a distant historical past to which they bear no inherent relation.