As a large market share of electric vehicles (EVs) is expected in the transportation section, the high penetration of EVs in the power grid has placed new challenges on the power system planning and operation. Their negative impacts on energy supply, transformer deterioration, and peak demand increment are revealed. Therefore, control methods for integrating EVs into the power grid are developed to mitigate the negative effects and exploit the aggregated EVs as energy storage devices to provide ancillary services. In this chapter, the vehicle-to-grid (V2G) operation in modern power system and its control framework are first introduced, which combines communication and EV charging infrastructures. Then, three different operation modes of EVs integrated to the power grid are described, which consists of vehicle-to-home (V2H), vehicle-to-vehicle (V2V), and V2G. The modeling and the control methods for these three operation modes are given. The planning of EV charging infrastructure and the ancillary services provided by V2G are discussed.