Slugline
Also: scene heading · master scene heading
A slugline is the scene heading that opens every scene in a screenplay. It names whether the scene is interior or exterior, the location, and the time of day — for example, "INT. KITCHEN — NIGHT." Sluglines are set in all caps and tell the reader, and later the crew, exactly where and when the action happens.
A slugline (also called a scene heading) has three parts: the setup (INT. or EXT.), the location, and the time of day. It is always typed in uppercase and sits flush left, with a blank line above it.
INT. means the scene is indoors; EXT. means outdoors. INT./EXT. covers a scene that moves between the two — a conversation inside a moving car, say. The time of day is usually DAY or NIGHT, though writers also use specific markers like DAWN, DUSK, or CONTINUOUS.
Sluglines are how a script is broken down for scheduling and budgeting. A first assistant director strips every slugline to build the shooting schedule, which is why precision matters: "EXT. PARKING LOT — NIGHT" implies lighting and overtime that "INT. OFFICE — DAY" does not.
INT. DINER — NIGHT Rain streaks the window. SAM nurses a cold coffee. EXT. PARKING LOT — CONTINUOUS