This chapter describes the nature of multiplayer online games (MOG), including their foundation as online games, their unique technical infrastructure, and their global development and popularity. Online gaming has become an increasingly popular genre of new media activity that is consumed by gamers all over the world. It is broad in scope, involves various Internet-access technologies such as mobile phones, game consoles, tablets, and personal computers, and can be divided into different categories using various criteria. MOGs, or similar terms such as massively multiplayer/multiuser online (MMO), massively multiplayer online game (MMOG), massively multiplayer online role-playing games (MMORPG), and massively multiplayer online persistent world (MMOPW), are contemporary Internet-only, personal computer–based gaming applications that allow multiple geographically distributed users to engage and/or interact with each other in real-time. MOGs are highly sophisticated, networked multimedia and multimodal Internet technologies that can construct entertaining, simultaneous, persistent, and social virtual worlds for gamers.