Ingmar Bergman originally penned the script in 1964 under the title "The Cannibals". A serious bout of pneumonia led him to reconsider the project whilst lying in hospital; he deemed it to be potentially too expensive in concept and execution. Bergman revised the script idea into a more low budget piece to accompany Persona (1966).
Bergman defines "The Hour of the Wolf" as "The time between midnight and dawn when most people die, when sleep is deepest, when nightmares are most palatable. It is the hour when the sleepless are pursued by their sharpest anxieties, when ghosts and demons hold sway. The hour of the wolf is also the hour when most children are born." According to "Films in Review" critic Henry Hart in the U.S. it's about 4 a.m. when the body's resistance is least.