ESO is also the abbreviation for Ensemble Studios Online, Ensemble Studios' gaming connection site and matchmaking service, launched with the release of Age of Mythology. It is at this point still young when compared to Blizzard's

Ensemble Studios, whose titles made while not owned by Microsoft, were formerly published by Microsoft, and they are now are owned by Microsoft and therefore still published by Microsoft. Independently, they did not previously have the resources to purchase and operate such a site, and as such, previous titles such as Age of Empires and Age of Kings were routed through the MSN Gaming Zone.

ESO currently consists of several channels of chatting, automated matchmaking, four main game types, and advanced setup. Other types of games such as scenarios and games with cheats turned on are available through advanced setup, but the win and loss are not applied to the rating ladders from advanced setup. It also supports a friend and pest lists, and lacks a good system for private chatting, as it allows only for private messages rather than a private room.

On an average day, at any given time during offpeak hours, there are roughly 2000 people online and connected to ESO.