<P>Dramatically updating and extending the first edition, published in 1995, the secondedition of The Handbook of Brain Theory and Neural Networks presents the enormous progress made inrecent years in the many subfields related to the two great questions: How does the brain work? and,How can we build intelligent machines?Once again, the heart of the book is a set of almost 300articles covering the whole spectrum of topics in brain theory and neural networks. The first twoparts of the book, prepared by Michael Arbib, are designed to help readers orient themselves in thiswealth of material. Part I provides general background on brain modeling and on both biological andartificial neural networks. Part II consists of "Road Maps" to help readers steer through articlesin part III on specific topics of interest. The articles in part III are written so as to beaccessible to readers of diverse backgrounds. They are cross-referenced and provide lists ofpointers to Road Maps, background material, and related reading.The second edition greatly increasesthe coverage of models of fundamental neurobiology, cognitive neuroscience, and neural networkapproaches to language. It contains 287 articles, compared to the 266 in the first edition. Articleson topics from the first edition have been updated by the original authors or written anew by newauthors, and there are 106 articles on new topics.</P>