http://www.gameinformer.com/b/news/archive/2015/04/19/star-wars-rogue-one-is-a-prequel-will-follow-mission-to-steal-death-star-plans.aspx
A few details about Star Wars' 2016 film, Rogue One, have been revealed as part Star Wars Celebration 2015. It will take place before Star Wars: Episode IV – A New Hope.
It won't be a numbered entry in the Star Wars film pantheon and instead serves as a stand-a-lone anthology film. According to a recent panel covering the film with its director Gareth Edwards (Godzilla), it won't feature Jedis or special powers, and is instead being approached as a grounded war film. The only confirmed casting so far is Felicity Jones, who will be playing a Rebel soldier who is involved in the mission. Here's the movie's official, one-line description:
A band of resistance fighters unite for a daring mission to steal the Death Star plans in the Star Wars Anthology film, Rogue One.
The panel also showed a brief teaser for the movie (which has not begun shooting) showing a lone TIE fighter flying through a forested valley, panning up to reveal the Death Star seen through the clouds in the distance.