This systematic presentation of the parametric approach to child language considers the nature of the information the child must acquire according to the various linguistic theories. In doing so it sets out in detail the practical aspects of acquisitional research, addresses the challenges of working with children of different ages and backgrounds, and shows how the resulting data can be used to test theories of grammatical variation. It presents studies of the acquisition of syllable structure, empty categories, and wh-movement. The book is written for graduate students and advanced undergraduates taking courses on child language acquisition in linguistics, psychology, and cognitive science, and will be a useful reference for all researchers in child language acquisition in whatever field. The data sets on which the book draws freely available to students and researchers via a website maintained by the author.