It is told by a third-person omniscient narrator whose perspective shifts among the main characters. The novel contains five historical "interludes" about the town of Derry written in the first person from the perspective of Mike Hanlon.
It is written mainly in the past tense; however, the Derry interlude sections are in the present tense.
It refers to a prehistoric, interdimensional creature living in the sewers under Derry, Maine. The creature often appears in the guise of a clown, but it also takes the form of whatever its victim fears most. Sometimes the creature is a combination of monster and clown.