In order to make up for the deficiencies of centralized power production and distant transmission, microgrid becomes a hot topic of research in distributed energy systems in recent years, along with the increasing distributed generation systems, the improvement of information technologies, the development of the power market and the shock of serious blackouts. And they will play an important role during development of sustainable energy, electric utility deregulation and restructuring efforts. This paper gives a review on the key technologies for microgrids, including new power electronic, protection and communication technologies. Besides, planning, operation control, energy management, economic evaluation and simulation of microgrids are described.