Classification is a popular topic in typological, descriptive and theoretical linguistics. This volume is the first to deal specifically with the diachrony of linguistic systems of classification. It comprises original papers that examine the ways in which linguistic classification systems arise, change, and dissipate in both natural circumstances and in circumstances of attrition. The role of diffusion in such processes is explored, as well as the question of what can be diffused. The volume is not restricted to nominal systems of classification, but also includes papers dealing with the less well-known phenomenon of verbal classification. Languages from a wide spread of world regions are examined, including Africa, Amazonia, Australia, Eurasia, Oceania, and Mesoamerica. The volume will be of interest to linguistic typologists, descriptive linguists, historical linguists, and grammaticalization theorists.