In folklore, the witching hour or devil's hour is a time of night associated with supernatural events. Creatures such as witches, demons and ghosts are thought to appear and to be at their most powerful. Black magic is thought to be most effective at this time. In the Western Christian tradition, the hour between 3 and 4 a.m. was considered a period of peak supernatural activity, due to the absence of prayers in the canonical hours during this period. Women caught outside without sufficient reason during this time were sometimes executed on suspicion of witchcraft. The phrase "witching hour" was first recorded in 1835.

Psychological literature suggests that apparitional experiences and sensed presences are most common between the hours of 2 and 4 a.m., corresponding with a 3 a.m. peak in the amount of melatonin in the body.

The term may be used colloquially to refer to any period of bad luck, or in which something bad is seen as having a greater likelihood of occurring.