This book is intended as an introduction both to the principles and parameters framework (Chomsky, 1981) and to the second language (L2) acquisition of syntactic representations. Hawkins's basic aim is to present evidence for the view that L2 learners progressively build subconscious mental grammars (i.e., a syntactic system) guided by Universal Grammar—an innate, language-specific system. However, this volume is not just an introductory textbook presenting and summarizing the work of other researchers in this particular field. Indeed, the book has another major aim: Within the context of the most current debates on the L2 acquisition of syntactic knowledge, Hawkins introduces his own theory of L2 development, which he terms Modulated Structure Building.