Cryptonomicon is closer to the genres of historical fiction and contemporary techno-thriller than to the science fiction of Stephenson's two previous novels, Snow Crash and Diamond Age. It features fictionalized characterizations of such historical figures as Alan Turing, Albert Einstein, Douglas MacArthur, Winston Churchill, Isoroku Yamamoto, Karl Dönitz, Hermann Göring, and Ronald Reagan, as well as some highly technical and detailed descriptions of modern cryptography and information security, with discussions of prime numbers, modular arithmetic, and Van Eck phreaking.
According to Stephenson: The title is a play on Necronomicon, the title of a book mentioned in the stories of horror writer H. P. Lovecraft:
I wanted to give it a title a 17th-century book by a scholar would be likely to have. And that's how I came up with Cryptonomicon. I've heard the word Necronomicon bounced around. I haven't actually read the Lovecraft books, but clearly it's formed by analogy to that.
The novel's Cryptonomicon, described as a "cryptographer's bible", is a fictional book summarizing America's knowledge of cryptography and cryptanalysis. Begun by John Wilkins (the Cryptonomicon is mentioned in Quicksilver) and amended over time by William Friedman, Lawrence Waterhouse, and others, the Cryptonomicon is described by Katherine Hayles as "a kind of Kabala created by a Brotherhood of Code that stretches across centuries. To know its contents is to qualify as a Morlock among the Eloi, and the elite among the elite are those gifted enough actually to contribute to it."