Book excerpt: Valency patterns and valency orientation have been frequent topics of research under different perspectives, often poorly connected. Diachronic studies on these topics is even less systematic than synchronic ones. The papers in this book bring together two strands of research on valency, i.e. the description of valency patterns as worked out in the Leipzig Valency Classes Project (ValPaL), and the assessment of a language's basic valency and its possible orientation. Notably, the ValPaL does not provide diachronic information concerning the valency patterns investigated: one of the aims of the book is to supplement the available data with data from historical stages of languages, in order to make it profitably exploitable for diachronic research. In addition, new research on the diachrony of basic valency and valency alternations can deepen our understanding of mechanisms of language change and of the propensity of languages or language families to exploit different constructional patterns related to transitivity.