The movie was written by Robert L. Baird, Jill Culton, Peter Docter, Ralph Eggleston, Dan Gerson, Jeff Pidgeon, Rhett Reese, Jonathan Roberts and Andrew Stanton. It was directed by Peter Docter, David Silverman and Lee Unkrich.
It premiered on November 2, 2001 with the best opening ticket sales ever for an animated film and the 6th best of all time.
Warning: Wikipedia contains spoilers
Monsters. Inc. is about a power company using children's screams to generate electricity. There are many doors to children's rooms from their closets. The monsters come out of the closets and make the children scream, generating electricity for the monster world. The monsters think that if they are touched by a child then it is poisonous, so they have many safety precautions. There is a contest to see which monster can generate the most electricity, and, as in all Disney movies, there is one good one vs. one evil one.
Monsters, Inc. won the Academy Award for Best Song (Randy Newman for If I Didn't Have You). It was nominated for Best Animated Feature, Best Effects, Sound Effects Editing and Best Music, Original Score.
Part of the 1952 Chuck Jones cartoon Feed the Kitty was reanimated and included in this feature. Some of the "sets" in this film are also sets from the animated feature Toy Story.