The state-of-the-art knowledge about knowledge is contained within the MIT Encyclopedia of the Cognitive Sciences. Its 471 comprehensive entries cover topics as diverse as "Hemispheric Specialization," "Epiphenomenalism," and "Algorithms" in 1,000 to 1,500 words each, thoroughly cross-indexed and extensively referenced to launch further research. A few biographical entries are also included, highlighting such giants as Alan Turing and Santiago Ramón y Cajal. The editors selected their contributors well, assigning "Neurobiology of Consciousness" to Christof Koch and Francis Crick, for example. Even better, six longer essays introduce the Encyclopedia, each providing an overview of one of the six disciplines that overlap to form cognitive science: computational intelligence; culture, cognition, and evolution; linguistics and language; neurosciences; philosophy; and psychology. These are enormously helpful to the researcher, as they are general enough to allow easy entry but still meaty enough to be useful themselves and as pointers to specific entries. The MIT Encyclopedia of the Cognitive Sciences, while not a casual entry into the field, is an essential addition to the reference shelf for anyone seriously interested in AI, consciousness, or other aspects of natural and artificial brains.