The electrification of the transportation sector through the diffusion of plug-in electric vehicles (EVs), coupled with cleaner electricity generation, is considered a promising pathway to reduce air pollution from on-road vehicles and to strengthen energy security. The annual new EV sales increased 8-fold since 2011. However, the market share of EVs is still less than 1% in the new vehicle market. One of the significant barriers to large-scale adoption of EVs is the charging facilities. Well developed EV charging services are essential for the successful launch of electric vehicles and provide valuable vehicle-to-grid (V2G) services to the smart grid. On the other hand, unplanned charging brings instability, inefficiency and higher cost to the power grid and hinders the rise of clean transportation. This work focuses on the EV charging, including the methodology, development, and economy. In different contexts, the technologies of EV charging are presented. Both online and off-line approaches are discussed, in decentralized and centralized scenarios. The interaction between the EVs and the power grid is studied, in particular for the V2G services including load shifting, frequency regulation and spinning reserves. The indirect network effect between EVs and EV charging are illustrated. A stylized model for both the EV consumers and the charging facility investor is developed, including the EV price, the coverage of the charging stations, and the price of charging.