Marvel Studios announced today that the first Phase Three movie, Ant-Man has shifted from a November 6, 2015 release to July 31, 2015. This means Phase Three will kick off just a few short months after Phase Two comes to a close with The Avengers: Age of Ultron on May 1, 2015.
As of now, Ant-Man's only box office competitor is Fox's adaptation Miss Peregrine's Home for Peculiar Children, directed by Tim Burton. No story details have been confirmed, but it will likely tell the origin of Hank Pym's transformation into the title character.
Marvel is currently in production on Phase Two's Guardians of the Galaxy, with The Avengers: Age of Ultron likely to start shooting sometime in 2014.