A new press release trumpets the announcement (though "timing and details of the start of playtests will be provided at a later date"), and the firms have also released a slick new cinematic trailer that will whet your appetite for Tamriel over the course of its whopping six-minute run time.
TESO will make use of ZeniMax's megaserver technology to "avoid the hassle of shard selection." The game will also feature a built-in social network which the company says makes the new MMORPG "one of the most socially enabled games ever created." You can sign up for beta via the game's official website, and we've embedded the new trailer just past the break.
[Source: Bethesda press release]
[Update: ZeniMax has also uploaded an FAQ regarding the beta. Enjoy!]