The generation and control of REM sleep is a highly complex system where much remains to be uncovered. Research has begun to decipher the neuronal networks and molecular mechanisms implicated in REM sleep but the full extent of its function is an open question. Pierre-Hervé Luppi, PhD, University of Lyon, Lyon, France, outlines what is known about the potential roles of REM sleep based on biological discoveries and clinical observations. In babies and young children, there is an important role for REM sleep in building neural connections. Several functions for REM sleep have been proposed in adults including memory consolidation, mood regulation and stimulation of neural circuits. This interview took place during the European Academy of Neurology 2021 congress.