Deletions of the genes encoding the integrin αVβ8 (Itgav, Itgb8) have been shown to result in abnormal vascular development in the CNS, including prenatal and perinatal hemorrhage. Other work has indicated that a major function of this integrinin vivois to promote TGFβ activation. In this paper, we show thatItgb8mRNA is strongly expressed in murine Müller glia and retinal ganglion cells, but not astrocytes. We further show thatItgb8deletion in the entire retina severely perturbs development of the murine retinal vasculature, elevating vascular branch point density and vascular coverage in the superficial vascular plexus, while severely impairing formation of the deep vascular plexus. The stability of the mutant vasculature is also impaired as assessed by the presence of hemorrhage and vascular basal lamina sleeves lacking endothelial cells. Specific deletion ofItgb8in Müller glia and neurons, but not deletion in astrocytes, recapitulates the phenotype observed followingItgb8in the entire retina. Consistent with αVβ8's role in TGFβ1 activation, we show that retinal deletion ofTgfb1results in very similar retinal vascular abnormalities. The vascular deficits appear to reflect impaired TGFβ signaling in vascular endothelial cells because retinal deletion ofItgb8reduces phospho-SMAD3 in endothelial cells and endothelial cell-specific deletion of theTGFβRIIgene recapitulates the major deficits observed in theItgb8andTGFβ1mutants. Of special interest, the retinal vascular phenotypes observed in each mutant are remarkably similar to those of others following inhibition of neuropilin-1, a receptor previously implicated in TGFβ activation and signaling.