This study characterizes the central projections of melanopsin-expressing retinal ganglion cells (mRGCs) in mice. These cells, which are directly photosensitive, project to multiple brain regions, including the suprachiasmatic nucleus (SCN), intergeniculate leaflet (IGL), olivary pretectal nucleus (OPN), ventral lateral geniculate nucleus (LGv), preoptic area, and several hypothalamic and limbic structures. Using gene-targeted mice expressing β-galactosidase in mRGCs, the researchers visualized these projections and confirmed their widespread distribution. The projections were predominantly crossed, except for the SCN, which received bilaterally symmetric input. Co-staining with cholera toxin B subunit showed that mRGCs provide most of the retinal input to the SCN, IGL, and lateral habenula, and significant input to the OPN. Other ganglion cells also contribute to these targets. Monocular enucleation revealed that mRGC projections are mostly crossed, with the exception of the SCN. The study also identified additional targets, including the lateral nucleus, peri-supraoptic nucleus, subparaventricular zone, medial amygdala, margin of the lateral habenula, posterior limitans nucleus, superior colliculus, and periaqueductal gray. The findings suggest that mRGCs play a key role in circadian regulation and pupillary reflexes, and that their projections are more extensive than previously recognized. The study highlights the importance of mRGCs in the visual system's non-image-forming functions and their potential role in various brain regions beyond the classical retinohypothalamic tract.This study characterizes the central projections of melanopsin-expressing retinal ganglion cells (mRGCs) in mice. These cells, which are directly photosensitive, project to multiple brain regions, including the suprachiasmatic nucleus (SCN), intergeniculate leaflet (IGL), olivary pretectal nucleus (OPN), ventral lateral geniculate nucleus (LGv), preoptic area, and several hypothalamic and limbic structures. Using gene-targeted mice expressing β-galactosidase in mRGCs, the researchers visualized these projections and confirmed their widespread distribution. The projections were predominantly crossed, except for the SCN, which received bilaterally symmetric input. Co-staining with cholera toxin B subunit showed that mRGCs provide most of the retinal input to the SCN, IGL, and lateral habenula, and significant input to the OPN. Other ganglion cells also contribute to these targets. Monocular enucleation revealed that mRGC projections are mostly crossed, with the exception of the SCN. The study also identified additional targets, including the lateral nucleus, peri-supraoptic nucleus, subparaventricular zone, medial amygdala, margin of the lateral habenula, posterior limitans nucleus, superior colliculus, and periaqueductal gray. The findings suggest that mRGCs play a key role in circadian regulation and pupillary reflexes, and that their projections are more extensive than previously recognized. The study highlights the importance of mRGCs in the visual system's non-image-forming functions and their potential role in various brain regions beyond the classical retinohypothalamic tract.