How and why does the sleeping brain generate dreams? Though the question is old, a paradigm shift is occurring in the science of sleep and dreaming that is making room for new answers. From brainstem-based models of sleep cycle control, research is moving towards combined brainstem/forebrain models of sleep cognition itself. This book presents five papers by scientists at the centre of the debate, and more than 75 commentaries on those papers by nearly all of the other leading authorities in the field. Topics include mechanisms of dreaming and REM sleep, memory consolidation in REM sleep and an evolutionary hypothesis of the function of dreaming. The papers and commentaries, together with the authors' rejoinders, represent a leap forward in our understanding of the sleeping and dreaming brain. The book's multidisciplinary perspective is intended for students and researchers in neuroscience, cognitive science and psychology.