In this outstanding collection of new work the methods and theories of formal syntax are focussed on grammatical variation and change. The editors open the volume with an extensive and accessible introduction to the ideas and techniques deployed in the book and the phenomena and issues on which they are brought to bear. Seventeen chapters follow, divided into two parts, the first concerned with grammaticalization and the second with parametric variation. These show what the application of contemporary theories of syntax and language variation can reveal about syntactic change and variation and the processes of parametric change which lie behind them. They also demonstrate the value of testing and constructing synchronic theories on the basis of historical data. The analyses range over many languages and language families, including Germanic, Romance, Greek, and Chinese. This book will interest scholars and students of grammatical change and theory at graduate level and above.