Michael Morris Rosbash is an American geneticist and chronobiologist, the Peter Gruber Endowed Chair in Neuroscience at Brandeis University and an Investigator of the Howard Hughes Medical Institute. He shared the 2017 Nobel Prize in Physiology or Medicine with Jeffrey C. Hall and Michael W. Young for elucidating the molecular mechanisms that govern the circadian rhythm. In their landmark collaboration at Brandeis, Rosbash and Hall cloned the period (per) gene and, in 1990, articulated the transcription-translation negative-feedback loop model in which the PER protein periodically inhibits the transcription of its own gene, producing self-sustaining roughly twenty-four-hour oscillations. Rosbash's group went on to identify additional clock components and regulatory layers, including the role of the transcription factors CLOCK and CYCLE and the contribution of post-transcriptional and RNA-processing control to clock function, drawing on his deep expertise in RNA biology and gene expression. This work transformed circadian rhythms from a descriptive phenomenon into a precisely defined molecular circuit conserved from flies to humans, with direct implications for sleep disorders, metabolic disease, jet lag and the timing of drug delivery. A member of the National Academy of Sciences and recipient of the Gruber Prize in Neuroscience (2009), Rosbash runs a laboratory whose circadian and RNA-biology toolkit makes it a natural counterpart for suppliers of gene-expression assays, fly-genetics reagents, imaging systems and behavioral-monitoring platforms.