For those of you who don't know, Episide IV: A New Hope - the original Star Wars - was released on May 25th, 1977 - so this looks to be a massive (almost) 40th Anniversary Release!
Little is known about his new title, but it will star Felicity Jones (The Theory of Everything).
Here is what starwars.com has to say...
Rogue One is the title for the first film in a unique series of big-screen adventures that explores the characters and events beyond the core Star Wars saga. Rogue One will be directed by Gareth Edwards (Monsters, Godzilla) and written by Oscar nominee Chris Weitz (Cinderella, About a Boy, Antz). The first actress cast is Felicity Jones, who garnered an Academy Award nomination and critical acclaim for her performance in The Theory of Everything.
The idea for the story of Rogue One came from John Knoll, an Academy Award-winning visual effects supervisor and chief creative officer at Industrial Light & Magic. He will executive produce along with Simon Emanuel (The Dark Knight Rises, Fast & Furious 6) and Jason McGatlin (Tintin, War of the Worlds). Kathleen Kennedy and Tony To (Band of Brothers, The Pacific) are on board to produce and John Swartz (Star Wars: The Force Awakens) will co-produce. The film starts shooting this summer in London and is due for release on December 16, 2016.