The articles collected in this book are concerned with the issues of restrictiveness and learnability within generative grammar, specifically, within Chomsky's 'Extended Standard Theory'. These issues have been central to syntactic research for decades and they are even more central w as results on syntactic theory, on learnability, and on acquisition begin to converge. I hope that this book can provide researchers in all of these areas with some insight into the evolution of ideas about these issues. The articles appear in their original form, with the following exceptions: A few typographical and other mir errors have been corrected; bibliog- raphic references have been updated and a unified bibliography provided. I would like to take this opportunity to ackwledge my vast intellec- tual debt to Noam Chomsky. My research would t have been possible without his work, his advice, and his guidance. Next, I offer deep thanks to Chomsky and my other co-authors represented here: Bob Fiengo, Joe Kupin, Bob Freidin, and Mamoru Saito. I am grateful, indeed, for the opportunity to collaborate with such outstanding linguists, and, more immediately, for their permission to reprint their co-authored articles. I also offer general thanks to the holders of the copyrights of the reprinted material. Specific ackwledgements appear on a separate page.