Book excerpt: Brain Facts is a primer on the brain and nervous system, published by the Society for Neuroscience. Brain Facts is a valuable resource for educators, students, and anyone interesting in learning about neuroscience. Download an audio recording of Brain Facts today, available on BrainFacts.org and through iTunes U. The brain is the most complex biological structure in the known universe. It is a topic rich with exciting new discoveries, continuing profound unknowns, and critical implications for individuals, families, and societies. Learn more about the brain and nervous system through articles, images, videos, and more on BrainFacts.org, a public information initiative of The Kavli Foundation, the Gatsby Charitable Foundation, and the Society for Neuroscience.