This monograph is an empirical study of a particular type of grammatical variation - genitive variation in English. Comparing the results of a Modern English experimental study and historical evidence for the development of genitive variation, the main empirical finding of this study is that the s-genitive has become more productive again from late Middle to Modern English. A new theoretical approach to grammatical variation is proposed which places the choice of genitive construction into the mind of individual language users and, in so doing, tries to account for the observed change.