"Avatar" doesn't open in theaters until Dec. 18 but the publicity campaign has set sail, in "Titanic" fashion. On Aug. 21, Twentieth Century Fox and director James Cameron will debut the movie's trailer (or preview) and select regular and IMAX theaters will screen extended footage. No word just yet on where those venues will be.

The worldwide trailer launch will be in all formats -- IMAX 3-D, IMAX 2-D, digital 3-D, digital 2-D and 35mm 2-D -- and folks not headed to the theater will be able to find the preview online.

"Avatar" is the story of an ex-Marine who finds himself thrust into hostilities on an alien planet filled with exotic life forms. As an Avatar, a human mind in an alien body, he finds himself torn between two worlds, in a fight for his own survival and that of the indigenous people.

"Avatar" stars Sam Worthington, Zoe Saldana, Stephen Lang, Michelle Rodriguez and Sigourney Weaver. Cameron, who has spent more than a decade on the film, showed 24 minutes of footage of "Avatar" at the just-concluded Comic-Con in San Diego and wowed the crowds.

Cameron is best known as the director of "Titantic," the highest-grossing movie of all time and winner of 11 Academy Awards.

Also on Aug. 21, being modestly dubbed "Avatar Day," Ubisoft will unveil the trailer for its video game, "James Cameron's Avatar: The Game," and Mattel will reveal the action figures for the film's Avatar and alien Na'vi characters.