Cloud gaming-as-a-service is emerging as one of the potential revenue generating futuristic fields with a higher growth rate. Cloud gaming service is an entertainment service that depends totally on the cloud computing technology. Cloud gaming delivers games to the gamers, anywhere at any time without any gaming specific hardware and without diminishing the gamer's quality of experience. From getting the user command to rendering the graphics, everything is processed at the gaming service provider end. The only need for the gamer is to use a thin client like web browser to access the cloud game server. In this chapter, we have detailed about the cloud game systems, cloud game services, issues in cloud gaming, economics of cloud gaming, research prospects and the evolution of cloud gaming service.