Pericytes were originally discovered and named more than hundred years ago as contractile cells around the blood vessel endothelial cells. Due to the lack of exclusive markers, pericytes are now defined by a combination of location, morphology and gene expression. Pericytes are attracting increasing attention as important regulators during development and during normal and disturbed organ function. In recent years, remarkable progress has been made in the identification and characterization of pericytes subpopulations and their amazing functions using state-of-art techniques. These advantages facilitated identification of molecular basis of interaction between these cells with several other more well studied cell types, and revealed key signals derived from pericytes involved in homeostasis, regeneration, and disease regulation. In the last ten years, several unexpected roles of pericytes have been discovered. It has been demonstrated that pericytes from different tissues differ in their properties as well as functions. Even more, pericytes are heterogeneous also within the same organ. This book is will describe the major contributions of pericytes to different organs biology in physiological and pathological conditions.