Well known for their work in first language (L1) acquisition, Crain and Thornton (henceforth C&T) have produced with their Investigations in Universal Grammar a thorough review of the innovative experimental techniques they developed to investigate the acquisition of syntax. In this sense, the volume would appear to be a kind of research-methods book. The volume is a great deal more, however. Indeed, in the volume's three main sections (16, 8, and 16 chapters, respectively), C&T present examinations not only of the nature of human-language grammars but also of the factors that conspire to result in linguistic performance. What makes the C&T volume superior is that they integrate theoretical framework with methodological practice so seamlessly.