Olga Fischer presents a critical analysis of morphosyntactic change and the mechanisms that trigger it. She shows how changes in discourse, lexicon, semantics, pragmatics, and sound interact with changes in morphosyntax, and considers the interface between the internal and external factors of change. She reveals how rates and speed of change in morphosyntax can be used to explore the degree to which grammar is innate or learned. Her book will be of central interest and value to students of linguistic change, at graduate level and above.