Current-generation Massively Multiplayer Online Games (MMOG), such as World of Warcraft, Eve Online, and Second Life are mainly built on distributed client-server architectures with server allocation based on sharding, static geographical partitioning, dynamic micro-cell scheme, or optimal server for placing a virtual region according to the geographical dispersion of players. This paper reviews various approaches on data replication and region partitioning. Management of areas of interest (field of vision) is discussed, which reduces processing load dramatically by updating players only with those events that occur within their area of interest. This can be managed either through static geographical partitioning on the basis of the assumption that players in one region do not see/interact with players in other regions, or behavioural modelling based on players’ behaviours. The authors investigate data storage and synchronisation methods for MMOG databases, mainly on relational databases. Several attempts of peer to peer (P2P) architectures and protocols for MMOGs are reviewed, and critical issues such as cheat prevention on P2P MMOGs are highlighted.