Good Omens: The Nice and Accurate Prophecies of Agnes Nutter, Witch (1990) is a fantasy novel written in collaboration between Terry Pratchett and Neil Gaiman. Due to the different status of the two authors in the United States and the United Kingdom, American editions credit Gaiman before Pratchett, while British editions credit Pratchett before Gaiman.

The book is a comedy and a somewhat parody of the 1976 film The Omen (as well as other books and films of the genre), concerning the birth of the son of Satan, the coming of the End Times and the attempts of the angel Aziraphale and the demon Crowley to avert them, having become accustomed to their comfortable postings in the human world. A subplot features the gathering of the four horsemen of the Apocalypse — War, Famine, Pollution (Pestilence having retired upon the invention of penicillin), and Death — the last of whom is characterised in a manner reminiscent of the personification of Death in Pratchett's Discworld novels and calls himself Azrael before his final exit.

Speculation as regards which author wrote what has been rife for many years. In an attempt to put the issue to rest, Neil Gaiman has said: "We were both living in England when we wrote it. At an educated guess, although neither of us ever counted, Terry probably wrote around 60,000 "raw" and I wrote 45,000 "raw" words of Good Omens, with, on the whole, Terry taking more of the plot with Adam and the Them in, and me doing more of the stuff that was slightly more tangential to the story, except that broke down pretty quickly and when we got towards the end we swapped characters so that we'd both written everyone by the time it was done, but then we also rewrote and footnoted each others bits as we went along, and rolled up our sleeves to take the first draft to the second (quite a lot of words), and by the end of it, neither of us was entirely certain who had written what. It was indeed plotted in long daily phone calls, and we would post floppy disks (and this was back in 1988 when floppy disks really were pretty darn floppy) back and forth." ^*