Back in May, director James Cameron revealed he will only make Avatar movies from now on, teasing that Avatar 4 may happen after shooting Avatar 2 and Avatar 3. Producer Jon Landau recently confirmed that Avatar 2 and Avatar 3 will be shot back-to-back, but there are no plans for Avatar 4.
"We are doing two back-to-back, but not a third."
Actress Sigourney Weaver revealed in June that production on the sequels will begin sometime this fall. Avatar 2 and Avatar 3 were initially scheduled for release in December 2014 and December 2015. However, Jon Landau revealed in April that they may not make those proposed release dates. As of now, all we know is Avatar 2 and Avatar 3 are actually happening. When these Pandora-set sequels hit theaters is still uncertain.