 Questions about dreaming in different areas of philosophy such as epistemology, ontology, philosophy of mind and cognitive science, and ethics are closely intertwined. Scientific evidence from sleep and dream research can meaningfully inform the philosophical discussion and has often done so in the past. The discussion of dreaming has also often functioned as a lens on broader questions about knowledge, morality, consciousness, and self. Long a marginalized area, the philosophy of dreaming and of sleep is central to important philosophical questions and increasingly plays an important role in interdisciplinary consciousness research, for example in the search for the neural correlates of conscious states, in conscious state taxonomies, and in research on the minimal conditions for phenomenal selfhood and conscious experience.