Fahrenheit 451 is often thought of as Bradbury's first true novel, his previous full-length fiction (The Martian Chronicles) being constructed from a set of short stories. In fact, Fahrenheit 451 also has its origins in Bradbury's short fiction.
Between 1948 and 1950, Bradbury wrote a number of short stories which have a clear thematic connection with Fahrenheit 451:
"Carnival of Madness" has its roots in an unpublished story called "The Castle", which previews "Carnival of Madness" closely, but is a completely different text.
In the late 1940s, Bradbury began work on a novel entitled Where Ignorant Armies Clash By Night. The fragmentary manuscript of this unpublished novel still exists. In Ray Bradbury: A Life of Fiction, William Touponce examines how the Assassin of that manuscript evolved into the Fireman of Bradbury's novella "The Fireman" (first published in 1951), and subsequently of its expanded form, the novel Fahrenheit 451. Bradbury was, of course, strongly motivated to write Fahrenheit 451 by the McCarthyist mood of the times.
Bradbury himself has said that his short story "The Pedestrian" (written in 1950, and first published in 1951) was a catalyst in developing Fahrenheit 451: he imagined his pedestrian turning a corner and encountering Clarisse...who is herself a vital catalyst within the novel.
As for the mechanics of it all, Bradbury claims to have spent $9.80 in dimes, hiring a typewriter in the basement of UCLA, at the rate of a dime per half-hour.
Bradbury has adapted his novel into a play, seen it adapted for radio and film, and has written screenplays for unrealised movie versions. In the 1950s, he successfully sued over Playhouse 90's plagiarised TV adaptation "Sound of a Different Drummer".
Eller, J. (2004) Personal correspondence
Bradbury, R. (1994) Zen in the Art of Writing. Santa Barbara, Ca.: Joshua Odell]