Pikmin 3 is the upcoming third installment in the Pikmin franchise revealed during the Nintendo press conference at the 2012 Electronic Entertainment Expo on June 5th. It will be released on the Nintendo Wii U console in spring 2013 for Japan, and sometime in quarter two 2013 elsewhere.
From what has been seen at E3 so far[1], Pikmin 3 revolves around 3 entirely-new characters who come to the Planet of the Pikmin for currently unknown reasons, and explore the depths of the planet after having become lost. None of these characters seem to be related to Olimar nor presumably Louie, who are notably missing, though Olimar was confirmed to indeed appear in the game.[2]
According to Krysta Yang, Public Relations Specialist for Nintendo, more of the story will be revealed as the game comes closer to launch. [3]
The game is planned to be more similar to Pikmin 1 due to the fact that Shigeru Miyamoto intends to add a time limit back to the plot. [4]
Pikmin 3 is the upcoming third installment in the Pikmin
franchise revealed during the Nintendo press conference at the 2012
Electronic Entertainment Expo on June 5th. It will be released on the
Nintendo Wii U console in spring 2013 for Japan, and sometime in quarter two 2013 elsewhere.
Plot

The three leaders we have seen so far in-game.From what has been seen at E3 so far[1], Pikmin 3 revolves around 3 entirely-new characters who come to the Planet of the Pikmin
for currently unknown reasons, and explore the depths of the planet
after having become lost. None of these characters seem to be related to
Olimar nor presumably Louie, who are notably missing, though Olimar was confirmed to indeed appear in the game.[2]
According to Krysta Yang, Public Relations Specialist for Nintendo,
more of the story will be revealed as the game comes closer to launch. [3]
The game is planned to be more similar to Pikmin 1 due to the fact that Shigeru Miyamoto intends to add a time limit back to the plot. [4]
From the wiki.