This paper considers the development of the alcohol and drug categories in the mental disorders section of successive editions of the International Classifications of Diseases, and the current definitions of the key categories. With respect to "dependence", it is argued that the concept was originally defined with respect to culturally close societies, but even between those societies there remain differences in nuance; that in current definitions dependence is not unitary; that there are difficulties in applying the concept across drugs; that technical definitions have drifted far from lay concepts; and that there are substantial questions about its cross-cultural applicability. As practitioners struggle to keep up with the shifts in nosological terminology and definitions over the last 30 years, the terms and criteria may well be quite vague in application despite their concreteness in appearance.