A long, long time ago in a galaxy far far away…
No, wait. Wrong movie.
In a time not too far from now in this very galaxy, on this very planet, humans have trashed the place so badly that they flee into space and leave an army of Waste Allocation Load Lifters—Earth class (that's WALL-E to you) to clean the place up.
It doesn't quite work.
One rusty little WALL-E remains 700 years later, trundling across the barren landscape and compacting all the trash that still exists. (Is nothing biodegradable?) WALL-E is lonely, with only a cockroach and his Hello, Dolly VHS tape to keep him company. He looks to the stars and dreams of love.
And—boom—one day love appears in the form of a sleek hovering egg-shaped robot named EVE. She's feisty: she spends her time blowing up oil tankers and, on a couple of occasions, almost annihilating WALL-E, too. But WALL-E takes EVE to his shelter to show off his collection in the hopes of winning her heart.
Or at least her circuit boards.
When WALL-E shows EVE a plant he found, she takes it and shuts down, sending a signal into space. When a ship retrieves EVE, WALL-E hitches a ride and ends up on the Axiom, the ship that all the humans left on 700 years ago. In the last 700 years, they've gotten incredibly lazy and incredibly obese. They can't even walk.
EVE and WALL-E take the plant to the Captain of the Axiom. The plant, which proves Earth is inhabitable again, will allow the Axiom to return to Earth and repopulate it. But when they open EVE… it's gone.
EVE and WALL-E are chucked into the Repair Ward, but they break out to find the plant.
It turns out that AUTO, the ship's wheel, had his GO-4 bot put the plant on a Life Pod and set it to self-destruct. WALL-E and EVE get it back and race to return it to the Captain's bridge. When they do, AUTO takes the plant away, saying that directive A113 forbids him from letting the Axiom return to Earth. He zaps WALL-E, frying his circuit board and chucks him in the dump.
EVE rescues WALL-E, but he's so fried that she needs to repair him. All his spare parts are on Earth, so EVE, with the help of the Captain (who fights AUTO and turns him off) returns the plant to the holo-detector, sending the Axiom back to Earth. On Earth, EVE repairs WALL-E...but his memories are erased.
But (guys, it's Disney, come on) EVE's spark of a kiss restores WALL-E's memories.
All the robots and fat humans step out of the Axiom and get ready to farm and dance and live life again on Earth.