This chapter focuses on the renal microcirculation. The microcirculation of the kidney is particularly intriguing because optimum regulation of renal microcirculatory dynamics is essential for the appropriate control of the intracapillary and interstitial forces that determine glomerular filtration, reabsorption of salt and fluid from the renal interstitium back into the vascular compartment, and the regulation of the medullary concentration gradient. There continues to be intense interest on many aspects regarding the physiology of the renal microcirculation. This is largely attributable to the cardinal role of the kidneys in the regulation of body fluid volumes and sodium balance which influences the cardiovascular system and the regulation of arterial pressure. While it is certainly recognized that the sophisticated regulation of transport processes, subject to redundant and robust regulatory mechanisms in all the nephron segments, are ultimately responsible for regulating excretory function, these processes are dependent on optimal control of regional perfusion and interstitial forces within the kidney. There are intimate interactions between the microcirculation and tubular transport processes. The emerging data provides mounting evidence that many intrinsic and extrinsic signaling mechanisms and paracrine systems exert dual roles to regulate both vascular tone and epithelial transport function responsible for solute and water handling, leading to synergistic actions which have powerful effects. Paracrine and hormonal agents which exert predominant vasoconstrictor effects also stimulate reabsorptive processes to enhance recovery of salt and water, while those which exert vasodilator actions reduce reabsorption and oxygen demand. © 2008 Elsevier Inc. All rights reserved.