Designers were sketching the movie's bizarre alien world, and the humans who visit it, for years before the movie became a reality. Creature designer Wayne Barlowe says he first met with Cameron in 1996:

At that time he was working hard on Titanic, but Avatar was more than a glimmer in his eye. He had an incredible, fully realized scriptment at hand that I read and fell in love with. The world of Pandora was already fully conceived and populated in Jim's mind.

In 2005, Barlowe spent four months at Cameron's house in Malibu, along with creature designer Neville Page (the man who gave us the Cloverfield monster) and two other designers. Cameron was gone for weeks at a stretch, because he was making a documentary about the Titanic. Page recalls,

He would come in, plant the seeds, go away for a bit, then come back. What he was doing while we were getting rolling [was] he was filming that special about the Titanic, where they were looking for the baths on the Titanic. It was a special research trip he was doing with the Discovery Channel. [We'd be] working late at Jim's house, and having him come back after a three week spell of being down at the freaking Titanic, and having him tell us a story [about being on the ocean floor].

Avatar Started As A Four-Month, Late-Night Jam Session At James Cameron's House

All in all, Page worked on Avatar nonstop for three years, an unimaginably long time for a designer to be attached to a single movie. And there were times, early in the process, when Page thought Avatar might never get made. Says Page, "There were a couple of times when I thought, 'Eh, is it really going to happen?' But after a while, you don't really care, because — I mean, you care, because you want the movie to be realized — but what a great job, to be hired to design cool stuff all day long."

Talking to these designers, a picture emerges of a freewheeling environment, where different designers took a crack at different creatures or machines, and no idea was too weird to try out. At the same time, Cameron started the project with a really clear image of what he wanted everything to look like. Says concept artist Ryan Church:

Jim definitely had strong ideas about the look of everything, he's a superb designer himself and could've designed the whole movie himself if he'd had the time. He did a ton of sketching himself. Sometimes he had a very specific description that needed only polishing and sometimes he knew exactly what it had to do and what impression it needed to convey but less of an idea of exactly the look.

Avatar Started As A Four-Month, Late-Night Jam Session At James Cameron's House

Cameron knew how the creatures on Pandora moved, how they ran with six legs or flew with four wings, and even how they breathed through a special opening.

Despite the huge crew of designers at work, Cameon's imaginary planet had to be consistent and have a unified "visual vocabulary" that "would imply both alien-ness and interspecies relationships that would convey a homogeneity suitable for another world," says Barlowe.

There were actually two different divisions in the Art Department, says concept artist James Clyne: "the division that worked on a lot of the flora and fauna of Pandora, and another part of the art department that worked more on the human machines, and the human factors." The movie also had two different production designers, Rick Carter and Robert Stromberg.