At global level, about 65% of water received as precipitation returns to the atmosphere as green water flow (i.e. transpiration from forest, grassland, wetland and rainfed farmland). Still, water management and governance to date has almost exclusively focused on the visible blue water flow (i.e. runoff flow in rivers, aquifers and lakes). Green water is defined as water flow returned to atmosphere in the original document. Only in the past few years has it become recognized as resources of production of plant biomass that first remain in the soil in the form of humidity, are then stored in plants during their growth, and are finally released back into the atmosphere through evaporation. This paper presented the evolution of the green water concept, the effects affect green water flow, and the roles of green water played in the terrestrial ecosystems, and reviewed the advances in green water evaluation and the current status of global green water resources and green water security. It is pointed out that green water resources should be included in the water resources evaluation system, green water related researches such as green water management, comprehensive usage of blue water and green water resources, and balancing water for humans and nature should be deployed in the future.