Normal development of all organs and maintenance of their physiological functions are critically dependent on vascularization. The quantity and quality of the vascularization are tightly controlled to meet the specific anatomical and physiological requirements of each organ. In fine-tuning the vascularization, blood vessels and their corresponding organ exchange chemical signals to control morphogenesis and homeostasis. Failure or malfunctioning of this “crosstalk” between the blood vessels and the organ can lead to disease conditions. Therefore, it is important to understand the molecular nature of this crosstalk, which underlies the development of future therapies.