The renal microvasculature is emerging as a key player in acute and chronic kidney diseases. Renal microvascular disease involves alterations in endothelial barrier permeability, exaggerated inflammation, impairment of endothelium-dependent vasorelaxation involving the nitric oxide system, increased oxidative stress, and loss of angiogenic factors. Moreover, evidence suggests that there is a microvascular component to the pathogenesis of renal scarring. New technology is being developed to explore renal microcirculation in vivo in experimental models and humans. This technology will provide a better understanding of the pathogenesis of kidney diseases and will help guide specific therapeutic strategies aimed at restoring the renal microcirculation. This article reviews the cellular and molecular mechanisms of renal microvascular dysfunction in acute and chronic kidney diseases and the potential diagnostic and therapeutic implications of these findings. Recent developments in the monitoring of renal microcirculation are described with respect to their advantages and limitations, and future directions are outlined. (C) 2015 by the National Kidney Foundation, Inc.