Consciousness is undoubtedly one of the last remaining scientific mysteries and hence one of the greatest contemporary scientific challenges. How does the brain's activity result in the rich phenomenology that characterizes our waking life? Are animals conscious? Why did consciousness evolve? How does science proceed to answer such questions? Can we define what consciousness is? Can we measure it? Can we use experimental results to further our understanding of disorders of consciousness, such as those seen in schizophrenia, delirium, or altered states of consciousness? These questions are at the heart of contemporary research in the domain. Answering them requires a fundamentally interdisciplinary approach that engages not only philosophers, but also neuroscientists and psychologists in a joint effort to develop novel approaches that reflect both the stunning recent advances in imaging methods as well as the continuing refinement of our concepts of consciousness. In this light, the Oxford Companion to Consciousness is the most complete authoritative survey of contemporary research on consciousness.