This is one of those stories that's been rumored for so long that the actual announcement is a bit shocking. Bethesda has officially announced The Elder Scrolls Online, which will be more formally revealed via the quaint format of a gaming magazine (remember those?) this month. The game will be developed by Zenimax Online rather than Bethesda itself, but one assumes that the Elder Scroll folks will be working closely with the developers.
Because of that print exclusive, there's not a lot of information released about the game at this point. The game will be set a millenium before the events of Skyrim, with players facing off against a powerful daedric prince. Players will apparently be able to adventure through the entire land of Tamriel, as well as participate in PvP between three factions. The game is currently slated to be released in 2013. There's sure to be more information released over the next month, so stay tuned.