According to an article on gamespot.com Edios made the official announcement via Twitter:
…Eidos Montreal, which today used the microblogging service to reveal the release date for Deus Ex: Human Revolution. Square Enix’s long-in-development action role-playing game will arrive on the PC, PlayStation 3, and Xbox 360 on August 23 in North America and August 26 in the UK.
But we knew this was coming, as Fanatical_g had written about the pre-tweet from Jean-François Dugas letting fans know they should know to look out for an official date announcement.
Mark your calendars, Deus Ex: Human Revolution is dropping on August 23rd