Brooks designed World War Z to follow the "laws" set up in his earlier work, The Zombie Survival Guide (2003), and explained that the guide may exist in the novel's fictional universe. The zombies of The Zombie Survival Guide are human bodies reanimated by an incurable virus (Solanum), devoid of intelligence, desirous solely of consuming living flesh, and cannot be killed unless the brain is destroyed. Decomposition will eventually set in, but this process takes longer than for an uninfected body and can be slowed by effects such as freezing. Although zombies do not tire and are as strong as the humans they infect, they are slow-moving and incapable of planning or cooperation in their attacks. Zombies usually reveal their presence by moaning.
Brooks discussed the cultural influences on the novel. He claimed inspiration from "The Good War": An Oral History of World War Two (1984) by Studs Terkel, stating: "[Terkel's book is] an oral history of World War II. I read it when I was a teenager and it's sat with me ever since. When I sat down to write World War Z: An Oral History of the Zombie War, I wanted it to be in the vein of an oral history." Brooks also cited renowned zombie film director George A. Romero as an influence and criticized The Return of the Living Dead films: "They cheapen zombies, make them silly and campy. They've done for the living dead what the old Batman TV show did for The Dark Knight." Brooks acknowledged making several references to popular culture in the novel, including one to alien robot franchise Transformers, but declined to identify the others so that readers could discover them independently.
Brooks conducted copious research while writing World War Z. The technology, politics, economics, culture, and military tactics were based on a variety of reference books and consultations with expert sources. Brooks also cites the U.S. Army as a reference on firearm statistics.