It is a horror novel by Stephen King. It is one of his best-selling books, and a favorite among his fans, though many critics have called it overly-long and uncompelling.

The novel is the story of seven friends from the fictional town of Derry, Maine, and is told with the narrative alternating between two different time periods. In the late 1950s, when they are eleven years old, the seven discover the existence of a child-murdering, shape-changing monster (which they call "It") and try to kill it. "It" appears in many forms, but normally as a clown called Pennywise. They make a pact to return and fight It again if It returns. All but one of them move away from Derry and begin to forget about the events, but one of them, town librarian Mike Hanlon, remains and calls them in 1985, when It begins to kill again. Five of Mike's friends return to finish killing the monster -- the sixth, Stanley Uris, is dead in his tub in Atlanta, having committed suicide moments after hanging up the phone.

All except Mike have gone on to success and wealth, though the stamp of their unhappy childhoods is evident: Beverley, the only girl in the group, is married to an abusive lout just like her father. Bill Denbrough married a woman who bears a striking resemblance to Bev. Eddie Kapsbrak married a large woman not unlike his overbearing mother.

Henry Bowers, the bully who once made their lives hell as kids, is also around; he was committed to an asylum nearly thirty years ago, and is goaded by It into escaping and returning to Derry to settle a few old scores.

It was filmed as a TV movie in 1990.