This chapter discusses the mystery of consciousness. A way to explore these mysteries is to ask how the brain mediates information processing, which brings us to the study of individual neurons and their relationship to neural systems. Systems neuroscience is the study of neural systems, which include those involved in vision, memory, language, emotion, somatosensory integration, and motor function. Consequently, the study of systems neuroscience emphasizes the identification of neural structures and events associated with the hierarchical steps in information processing. The prodigious growth of modern systems neuroscience is owed to the convergence of three key subdisciplines, each of which contributed major technical or conceptual advances to the understanding of information processing: neuropsychology, neuroanatomy, and neurophysiology. The chapter explores consciousness and evolution. It then describes the characteristics of consciousness. In the past 20 years, consciousness has been described and investigated with respect to three characteristics: unity, subjectivity, and prediction.