This chapter reviews studies of the prevalence and extent of common social dynamics in multiplayer online games (MOGs), endeavoring to better understand if and how a MOG's social components can explain its social nature, connect players' individual experiences to group activities, and contribute to the game's success. It also reviews five common social dynamics of most MOGs, namely, presence, communication, collaboration, conflict and competition, and community. These represent a spectrum of the increasingly rich and complicated game world. Communication in MOGs is different from either traditional face-to-face (FTF) communication or other types of communication technologies. In general, communication in MOGs is characteristic of both computer-mediated communication and avatar-mediated communication. Inhabiting a virtual environment and connected to others via computer-mediated and avatar-mediated communication, MOG players are able to conduct various social activities, of which collaboration is the dominant one.