This paper presents a detailed review of a vehicle-to-grid (V2G) technology, in conjunction with various charging strategies of electric vehicles (EVs), and analyzes their impacts on power distribution networks. It is shown in this study that a vehicle, equipped with the ability of a V2G application, offers various features such as regulation of active power, support for reactive power, load balancing, current harmonics filtering etc. However, the technology of V2G also creates challenging issues, for instance, degradation of batteries, communication overhead between an EV and a grid, changes in whole infrastructure of a distribution network. In particular, the impacts of the EVs that are based on their penetration levels and charging profiles are discussed in detail. Moreover, an extensive analysis is also presented on coordinated/un-coordinated charging, delayed charging, off-peak charging and intelligent scheduling in a distribution network (DN). Our study also shows that the economic benefits of a V2G technology heavily depend on the strategies of charging and vehicle aggregation.