If you are reading a screenplay for the first time, or just sitting down to write your first scene, those capital letters at the top of each scene can look like a code you were never given the key to. INT and EXT are abbreviations used in screenplay scene headings: INT stands for interior, and EXT stands for exterior. They tell the reader, the director, and every department head whether the action takes place inside or outside a physical location. That is the full answer. What follows is everything you need to use these abbreviations correctly and confidently.

Every scene in a properly formatted screenplay begins with a slug line, also called a scene heading. That heading has three parts: the INT or EXT designation, the specific location, and the time of day, all separated by hyphens. A correct slug line looks like this: INT. COFFEE SHOP - DAY or EXT. ROOFTOP - NIGHT. The period after INT or EXT is standard formatting. Most professional software adds it automatically, but if you are typing by hand, include it.

Why INT and EXT Matter Beyond Simple Location

These two letters do more than orient the reader. They drive production logistics. A scene labeled EXT tells the production team to scout an outdoor location, check weather windows, plan for natural light, and budget for potential rain days. A scene labeled INT triggers a different set of conversations: which stage or practical location, how to light an enclosed space, how to manage sound. When a producer reads a script, they are quietly counting EXT scenes because outdoor shoots are generally more expensive and unpredictable. If your thriller has forty exterior night scenes, that will register before a single meeting happens.

For writers, understanding this also sharpens your creative decisions. Every time you choose to put a scene outside when it could just as easily happen inside, you are making a production choice. That is not a reason to avoid exteriors, but it is a reason to be intentional about them.

How to Write the Full Scene Heading Correctly

The slug line follows a fixed pattern. Here is how each element works:

  • INT. or EXT. comes first, always in caps, always followed by a period.
  • The location follows after a space. Be specific enough to be useful: SARAH'S APARTMENT - KITCHEN is clearer than just APARTMENT. Specificity helps continuity departments and keeps your script from feeling vague.
  • The time of day closes the heading, separated by a hyphen. DAY and NIGHT are standard. DAWN, DUSK, CONTINUOUS, LATER, and MOMENTS LATER are also widely used. CONTINUOUS means the action flows without a time cut from the previous scene, which matters a great deal to editors.

The full slug line is always on its own line, in all caps, with no additional punctuation beyond the period after INT or EXT and the hyphen before the time. Double-check this in your formatting software before you send anything out.

What to Do When a Scene Is Both Inside and Outside

Real locations blur the line. A character stands in a doorway, half in the rain, half in the hallway. A car chase moves through a tunnel. A greenhouse is technically inside, but it feels like outside. Here is how working writers handle these situations:

  • INT/EXT. or EXT/INT. is an accepted convention for scenes that straddle both environments. A phone call where one character drives and another is at home, cutting between both, might use this designation. List the dominant environment first.
  • For a scene primarily inside a vehicle that is moving through an exterior location, most writers use INT. CAR - MOVING - DAY. The MOVING flag tells the crew the background will be in motion.
  • When in doubt, choose the environment where the camera will spend the most time, and let your action lines describe the rest.

Common Mistakes Writers Make With Slug Lines

The abbreviations themselves are rarely the problem. The mistakes usually live in the details around them:

  1. Inconsistent location names. If you call it INT. MARCUS'S OFFICE - DAY in scene 3 and INT. OFFICE - MARCUS - DAY in scene 47, your script's scene count and breakdown reports will treat these as two different locations. Pick a name and use it every time.
  2. Omitting the time of day. Some writers drop the time element, especially in early drafts. Do not. Even if you plan to fill it in later, a slug line without a time of day reads as incomplete and can confuse coverage readers.
  3. Overusing CONTINUOUS. CONTINUOUS is meaningful only when the geography connects scenes directly. Using it as a filler when no real continuous action is implied muddies your timeline.
  4. Writing a new slug line when you don't need one. If a character simply walks from the kitchen to the living room within the same INT scene, you do not need a new slug line unless you want to signal a meaningful location shift. Over-heading clutters the read.

How Slug Lines Affect the Reading Experience

Producers, agents, and script readers move through a screenplay quickly. Slug lines act as visual anchors that let the eye reset and locate the story in space. Clean, consistent headings make a script feel controlled and professional. Messy headings, even if every word of dialogue is brilliant, signal a writer who has not yet internalized the format. That is a fixable problem, but it costs you trust with the first reader.

If you are building strong formatting habits from the start, the article Writing a Screenplay in 90 Days: A Realistic Plan walks through how to structure your drafting process so format decisions like these become automatic rather than distracting.

Tools like Better Draft analyze your structure and flag formatting issues in your margins as you write, which means problems with inconsistent slug lines or missing time designations surface immediately rather than in a cold read weeks later.

A Few Edge Cases Worth Knowing

Some situations trip up even experienced writers:

  • Dreams and fantasy sequences. These still need slug lines with INT or EXT. Add a parenthetical or action line to signal the subjective nature of the scene, but the heading format does not change.
  • Phone calls. If you are intercutting between two locations, you can use INTERCUT WITH after establishing both locations separately, or use INT/EXT if one party is in a car. Either approach works; just be consistent across your script.
  • The word SCENE before the heading. You will sometimes see older scripts that use SCENE: or number their scenes explicitly. Numbered scenes appear in shooting scripts, not spec scripts. In a spec, leave scene numbers out entirely.
  • Archival footage, titles, and text on screen. These get their own formatting conventions and do not use INT or EXT headings. They are typically handled in all-caps action lines or with specific formatting your screenwriting software will support.

FAQ

Can I write EXT. for a scene set inside a building but near a window with a view?

No. The designation refers to where the camera and characters are physically located, not what they can see. If the scene takes place inside an office with a view of the city, it is INT. The window and the view outside are described in your action lines.

Does it matter if I write INT or INT. with a period?

Industry standard includes the period: INT. Most screenwriting software inserts it automatically. Omitting the period in a spec script is a minor issue, but matching standard formatting is always the safer choice because it signals familiarity with the form.

What does CONTINUOUS mean versus LATER in a slug line?

CONTINUOUS means the scene flows directly from the previous scene with no gap in time, often because a character physically moves from one space to another. LATER implies an unspecified amount of time has passed in the same location. Both are useful; use them precisely based on your story's actual timeline.

Where can I get feedback on whether my slug lines and formatting are correct?

Script coverage is one reliable option. A coverage report will often flag formatting issues alongside story notes. You can see what a professional report actually looks like in this breakdown: Script Coverage Example: What the Report Includes. For ongoing feedback as you draft, Better Draft's paid plans start at $16 per month and include structural analysis and margin notes that catch formatting problems in real time.