Rainbow Six seems to be getting a new game, titled "Rainbow Six: Patriots", in 2013.
Not much was revealed about the new game, other than being able to "capture the reality of modern-day terrorism" and that it won't be set in Las Vegas, where Rainbow Six: Vegas and Vegas 2 were set. However, it's still being developed by Ubisoft Montreal, the same devs behind Vegas, but is also getting help from Ubisoft Toronto and Ubisoft Red Storm.
There will also be multiple playable characters for the single player, and its said to be a "new direction" for the series narrative. The story involves elite force Team Rainbow as they face off against the revolutionary group True Patriots, who believe that the government is run by corporations. This is said to bring about "tough ethical decisions" for Team Rainbow in their quest to stop the terrorists.
Multiplayer will be co-op and competitive, much like Vegas, but will apparently feature new forms of communication and coordination.
Rainbow Six has been a long-standing popular FPS franchise since the late nineties. It has since gone through many sub series, the latest one of course being Vegas, but is most well known for its heavy reliance on teamwork and tactics as well as a good dose of realism. Rainbow Six: Vegas was met with positive reviews. Its sequel, however, was met with almost 10% lower reviews, criticized mainly for not bringing much new to the table.
No other info on Patriots is known outside of some minor art (which you can see at the source). The game is set for a Playstation 3, Xbox 360, and PC release in 2013.