Language change and language acquisition can be studied in terms of the development and/or reconstruction of grammatical forms. Both grammaticalization theory and certain approaches to language acquisition cast explanatory light on the process as sequential stages of re-analysis and re-encoding. Language history shows that both grammaticalization and acquisition are decisively influenced by the question of medium, notably the medium of written language. Against this background, the articles assembled here examine the emergence and acquisition of grammatical forms and points up both the similarities and the terminologically crucial distinctions between social genesis and language acquisition.