Typological hierarchies are widely perceived as one of the most important results of research on language universals and linguistic diversity. Explanations for typological hierarchies, however, are usually based on the synchronic properties of the patterns described by individual hierarchies, not the actual diachronic processes that give rise to these patterns cross-linguistically. This book aims to explore in what ways the investigation of such processes can further our understanding of typological hierarchies. To this end, diachronic evidence about the origins of several phenomena described by typological hierarchies is discussed for several languages by a number of leading scholars in typology, historical linguistics, and language documentation. This evidence suggests a rethinking of possible explanations for typological hierarchies, as well as the very notion of typological universals in general. For this reason, the book will be of interest not only to the broad typological community, but also historical linguists, cognitive linguists, and psycholinguists.