Premise: The Boogeyman is a supernatural monster that feeds on fear and lives in shadows -- primarily under beds and in closets. He emerges, grabs scaredy cats and does nasty things to them. Each film in the series, from producer Sam Raimi, features a different person dealing with the creature's evil ninja stylings.
Potential spoilers ahead!
As a child, Tim (Barry Watson) witnessed his father dragged into his closet and killed by the Boogeyman. Fifteen years later, he's called back to his childhood home by the death of his mother, having convinced himself that what he witnessed was all in his mind. However, he's soon haunted by visions of dead children -- presumably taken by the Boogeyman -- including a girl named Frannie who tells Tim that he has to face his fears back where his father was taken. Eventually, Tim gains enough courage to face the monster, a ghostly bald man in a trench coat. Tim takes a doll he's had since childhood that looks like the Boogeyman (for some reason) and smashes it, injuring the monster, who's then sucked into the closet world.
As children, siblings Laura and Henry saw their parents murdered by the Boogeyman, and for the past 10 years, they've been terrified of him. Henry found help at a psychiatric home for people suffering from irrational fears, and after he leaves, Laura decides to do the same. After she arrives, though, people start dying from the things they fear the most. The patients, thinking that Dr. Allen (Tobin Bell) is to blame, snoop through his files and find out that Tim (from the first film) ended up in his psychiatric care and killed himself. The killer turns out to be Henry, dressed up as the Boogeyman because the Boogeyman has no fear. Unlike the other two films in the series, this one is a non-supernatural slasher.
Audrey, the daughter of Boogeyman 2's Dr. Allen, is a college student who discovers her father's theory that his patients' faith in the existence of the Boogeyman could actually make the monster real. By reading this theory, Audrey's own belief brings the Boogeyman into reality. She seeks help from her friend Sarah, and when the monster kills Audrey and targets Sarah's circle of friends one by one, she becomes a believer. Belief in the Boogeyman grows in Sarah's dorm, empowering the creature even further, so Sarah ends up taking the blame for all of the deaths in order to dissipate the students' belief in the monster. However, as she's being taken away by the cops, she's grabbed by the Boogeyman, leaving the legend to remain.