Book excerpt: Research on creolization, language change, and language acquisition has been converging toward a triangulation of the constraints along which grammatical systems develop within individual speakers--and (viewed externally) across generations of speakers. The originality of this volume is in its comparison of various sorts of language development from a number of linguistic-theoretic and empirical perspectives, using data from both speech and gestural modalities and from a diversity of acquisition environments. In turn, this comparison yields fresh insights on the mental bases of language creation.The book is organized into five parts: creolization and acquisition; acquisition under exceptional circumstances; language processing and syntactic change; parameter setting in acquisition and through creolization and language change; and a concluding part integrating the contributors' observations and proposals into a series of commentaries on the state of the art in our understanding of language development, its role in creolization and diachrony, and implications for linguistic theory.Contributors : Dany Adone, Derek Bickerton, Adrienne Bruyn, Marie Coppola, Michel DeGraff, Viviane D�prez, Alison Henry, Judy Kegl, David Lightfoot, John S. Lumsden, Salikoko S. Mufwene, Pieter Muysken, Elissa L. Newport, Luigi Rizzi, Ian Roberts, Ann Senghas, Rex A. Sprouse, Denise Tangney, Anne Vainikka, Barbara S. Vance, Maaike Verrips.