The Martian Chronicles is a fixup of short stories with new text connecting them into a novel. Bradbury has credited Sherwood Anderson's Winesburg, Ohio and John Steinbeck's The Grapes of Wrath as influences on the structure of the book. He has called it a "half-cousin to a novel" and "a book of stories pretending to be a novel". As such, it is similar in structure to Bradbury's short story collection, The Illustrated Man, which also uses a thin frame story to link various unrelated short stories.
The Martian Chronicles follows a "future history" structure. The stories, complete in themselves, come together as episodes in a larger sequential narrative framework. The overall structure is in three parts, punctuated by two catastrophes: the near-extinction of the Martians and the parallel near-extinction of the human race.
The first third (set in the period from January 1999—April 2000) details the attempts of the Earthmen to reach Mars, and the various ways in which the Martians keep them from returning. In the crucial story, "—And the Moon be Still as Bright", it is revealed by the fourth exploratory expedition that the Martians have all but perished in a plague caused by germs brought by one of the previous expeditions. This unexpected development sets the stage for the second act (December 2001—November 2005), in which humans from Earth colonize the deserted planet, occasionally having contact with the few surviving Martians, but for the most part preoccupied with making Mars a second Earth. However, as war on Earth threatens, most of the settlers pack up and return home. A global nuclear war ensues, cutting off contact between Mars and Earth. The third act (December 2005—October 2026) deals with the aftermath of the war, and concludes with the prospect of the few surviving humans becoming the new Martians, a prospect already foreshadowed in "—And the Moon be Still as Bright", and which allows the book to return to its beginning.