Inside Out

Movie Title
Bleeding Cool published an article stating the name of Pete Docter's next film would be The Inside Out, but that has not been officially announced by either Disney or Pixar.

Updated Synopsis from CinemaCon 2012
Here is an updated synopsis from the Disney panel at CinemaCon on April 24, 2012: "Pixar takes audiences on incredible journeys into extraordinary worlds: from the darkest depths of the ocean to the top of the tepui mountains in South America; from the fictional metropolis of Monstropolis to a futuristic fantasy of outer space. From director Pete Docter (Up, Monsters, Inc.) and producer Jonas Rivera (Up), the inventive new film will take you to a place that everyone knows, but no one has ever seen: the world inside the human mind."

There is also good information that Michael Arndt is working on the script (from Big Screen Animation).

Details from John Lasseter
In an interview with Charlie Rose in early December 2011, John Lasseter gave details, about the upcoming film: It takes place in a girl's mind, and is about her emotions as characters.

More recently he made a similar statement to Bleeding Cool, and gave further details: "Pete [Docter] has this way of constantly trying to figure out something that we’re all familiar with in some way… he’s constantly looking for these kinds of things. You look at people oftentimes and they do something to make you go “What are they thinking?” or it’s like how a song gets stuck in your head and you just can’t get it out. Little quirky thing like this that we all do. Certain emotions just seem to take us over, anger or happiness, where you start giggling and laughing and you can’t stop. He thought “I want to take a look at that, explain that.” His idea is that the emotions of this little girl are the characters and it takes place in the head of this little girl, and shows how they control things that go on. It’s very, very clever and it’s truly unlike anything you’ve ever seen, yet it explains things you’ve seen."

Details Announced
Pixar revealed the following information on the film at D23 Expo 2011:

"From director Pete Docter comes an inventive new film that explores a world that everyone knows, but no one has seen: inside the human mind."

Directed by Pete Docter

Co-directed by Ronnie del Carmen

Produced by Jonas Rivera

(via The Pixar Blog)