It is horror originally published in 1986. I bought my copy new.
This review includes spoilers.
Review:
In 1985, six people receive a phone call from a childhood friend named Mike, asking them to come back to their hometown of Derry, Maine so that they can fulfill a promise they made. Until the moment of the phone call, none of them remembered either Mike or the promise they made, but most of them are able to overcome the shock of their gradually returning memories and make their way to Derry.
The seven members of the Losers Club first meet back in 1958, bound by their status as misfits and frequent targets of a bully named Henry Bowers. Bill, the leader of the group, has a bad stutter. His friend, Eddie, suffers from asthma and an overprotective mother. Ben is lonely and overweight, with a huge secret crush on Beverly. Beverly has an abusive father. Richie has a bad habit of letting his mouth run away with him. Stan is Jewish. The group is rounded out by Mike, who is Black.
One other thing binds the group together: they've all had terrifying unexplained experiences tied to some sort of malevolent being in Derry they call "It." It killed Bill's younger brother, George, as well as many other children in Derry, and there is evidence that It has been affecting Derry for a long time.
Somehow, in a way that none of the adult Losers Club members can quite remember until the time is right, they fought It. Unfortunately, they didn't quite manage to kill It. Now they need to make yet another attempt to defeat It, for good this time.