Root hairs are long tubular outgrowths from specialized epidermal cells of roots. Root hairs can in-crease the root surface area for aiding plants in nutrient and water acquisition. Development of root hairs in-cludes four phases:root hair cell fate speciifcation, root hair initiation, root hair tip growth and root hair matu-ration. This review represents cells morphology and the physiochemical changes in four phases of root hairs, followed by discussion about the molecular mechanisms of root hair cell fate specification, the regulatory mechanisms of TFs (EXPANSIN, bHLH and MYB) ROPs and auxin/ethylene on root hairs development.