Kubrik and Clarke wrote the screenplay, more or less, and Clarke wrote the novelization as the film was in production, IIRC, which is why there’s some discrepancies between the two (for instance, all the action happens around Saturn, not Jupiter, in the book, but Kubrik went with Jupiter because of difficulties filming the rings of Saturn believably). Pick up a recent copy of the book; Clarke has a good introduction that covers a lot of it (he has similar intros in each of the sequels — 2010 (much better than the film), 2061, and 3001 — that give some great background on the writing of the novel and the filmmaking process.