Allusions to other works
The novel has J. Edgar Hoover utterly intrigued by The Triumph of Death, a painting by Pieter Bruegel the Elder. Hoover first sees the painting while at the baseball game; the painting was reproduced in Life and pieces of it fall on him when someone in the stands above tears up the magazine and tosses the pieces. Later in the book he obtains a print of the painting.
Several segments of the novel are named in homage to other works. Das Kapital is Karl Marx's magnum opus, "Long Tall Sally" is a song by Little Richard also famous as a cover by The Beatles, and "Cocksucker Blues" is an infamous unreleased Rolling Stones song and film. "Better Things for Better Living Through Chemistry" was an advertising slogan for DuPont, while "The Cloud of Unknowing" is an anonymous work of Christian mysticism written in Middle English in the latter half of the 14th century.
Allusions to actual history, geography and current science
The novel incorporates a number of historical events. The prologue is about "The Shot Heard 'Round the World" and the whereabouts of the ball hit by Thomson are a recurrent element of the book. The book also employs Lenny Bruce’s reaction to the Cuban Missile Crisis and Soviet Union's atomic weapons program (including their testing grounds in Kazakhstan).
DeLillo has said that the front page of The New York Times on October 4, 1951, inspired Underworld.