Computer games, now a significant economic sector and subject to both academic and industry research and development, continue to grow in popularity at a substantial rate. Multiplayer networked games, which enable hundreds of thousands of players to simultaneously interact with each other, are now widely used not only just for entertainment, but also for socializing, business, commerce, scientific experimentation, and many other practical purposes. In this special issue, we focus on online games and cover scientific, engineering, and research topics in terms of systems and networking support to enable such games.