The Associated Press Stylebook and the Chicago Manual of Style are the two most influential style guides in American English publishing. Almost every newsroom uses AP. Almost every book publisher uses Chicago. They share most of their core philosophy — but the details of title-case capitalization differ in ways that produce noticeably different output. If you've ever wondered why a headline you wrote in one publication "feels off" in another, the answer is often these subtle rule differences.
Here's a thorough comparison, with real examples generated by our case converter so you can verify each claim yourself.
The headline difference
Take a single phrase and convert it under each style. Use the man with the golden gun.
- AP: The Man With the Golden Gun
- Chicago: The Man with the Golden Gun
The difference is the word with. AP capitalizes it because it's four letters long; AP's rule is to lowercase prepositions of three letters or fewer. Chicago lowercases it because Chicago lowercases all prepositions regardless of length.
This isn't an edge case. The two styles diverge constantly because English has many four-, five-, and six-letter prepositions: over, under, across, through, against, between, before, during, without. Every one of those gets capitalized in AP and lowercased in Chicago.
The full AP rule set
AP, per the most recent editions of the AP Stylebook, applies these rules to headlines, photo captions, and standing heads:
- Capitalize the first word and the last word.
- Capitalize all nouns, verbs (including is and other forms of to be), adjectives, adverbs, and pronouns.
- Lowercase articles: a, an, the.
- Lowercase coordinating conjunctions: and, but, or, nor, for, yet, so.
- Lowercase prepositions of three letters or fewer: at, by, in, of, on, to, up, as.
- Capitalize prepositions of four or more letters.
- Capitalize after a colon if a complete clause follows.
- Capitalize both parts of hyphenated compounds: State-of-the-Art.
The full Chicago rule set
Chicago, per the most recent edition of the Chicago Manual of Style, applies these rules to all titles of works (books, articles, songs, etc.) and to most section headings:
- Capitalize the first and last word.
- Capitalize all "major" words: nouns, pronouns, verbs (including is), adjectives, adverbs, and subordinating conjunctions (because, although, since, unless, when).
- Lowercase articles: a, an, the.
- Lowercase coordinating conjunctions: and, but, or, nor, for, yet, so.
- Lowercase all prepositions regardless of length.
- Capitalize after a colon.
- For hyphenated compounds, capitalize the major parts and lowercase articles, prepositions, and conjunctions within them: Self-Sustaining but Stand-up Comedy.
Why the preposition rule matters so much
The single biggest rule difference between AP and Chicago is the preposition treatment. Let's run through a few headlines so you can see the cumulative effect:
| Input | AP | Chicago |
|---|---|---|
| the road through the mountains | The Road Through the Mountains | The Road through the Mountains |
| between two worlds | Between Two Worlds | Between Two Worlds |
| life without limits | Life Without Limits | Life without Limits |
| the day after tomorrow | The Day After Tomorrow | The Day after Tomorrow |
Notice how between at the start of the title gets capitalized in both styles (first word rule), but after and without in the middle of the title diverge.
Which to use
The decision is almost entirely about audience and convention, not about which style is "better."
Use AP if you're writing for:
- A newsroom, wire service, or news website
- A corporate communications team — press releases, investor announcements, internal newsletters
- A marketing function that wants its headlines to look like journalism
- A college newspaper or journalism program
- Most digital publications that emerged from newsrooms (Bloomberg, Reuters, Politico, Axios)
Use Chicago if you're writing for:
- A book publisher (most university and trade presses)
- A humanities-focused magazine or journal
- Long-form non-fiction — essays, memoirs, biographies
- Academic publishing in history, philosophy, religious studies
- Most literary criticism and review publications
If you're a writer with no organizational style guide imposed on you and you have to choose, the most useful question is: do your readers expect newsroom voice or book-publishing voice? If you're producing news-like content with strong headlines, AP makes sense. If you're producing book-like content with long-form essays and a slower cadence, Chicago makes more sense.
What about web headlines specifically?
Most digital publications follow AP, even when their content is closer to magazine writing. The reason is practical: AP rules are simpler and produce more obviously "correct-looking" headlines in social media previews. Chicago's preposition rule, taken to its extreme, produces titles like The Way through the Woods that some readers parse as typos.
If you're starting a publication today and don't have strong reasons to pick Chicago, AP is the more common modern default for headlines specifically. Reserve Chicago for body copy, book titles within articles, and any references to long-form works.
Other things AP and Chicago disagree about
Title case is only one area where they differ. Some other notable splits:
- Oxford comma: Chicago requires it (red, white, and blue); AP omits it by default (red, white and blue). This is the most visible day-to-day difference.
- Numerals: AP spells out one through nine and uses numerals from 10 up. Chicago spells out one through one hundred, plus round hundreds.
- State abbreviations: AP uses traditional abbreviations (Calif., N.Y., Mass.). Chicago uses two-letter postal codes (CA, NY, MA).
- Title formatting in body copy: AP uses quotation marks for book titles ("To Kill a Mockingbird"); Chicago uses italics (To Kill a Mockingbird).
- Honorifics: AP drops most courtesy titles in subsequent references; Chicago retains them when appropriate to the context.
The title-case differences alone make these styles distinguishable to anyone who has read both consistently. If you've worked in a newsroom and then moved to book editing, the first thing you notice is that Chicago lowercases all those prepositions you spent years capitalizing.
Mixing styles within an organization
Some publications do this on purpose. The New Yorker, for example, follows its own house style that's closer to Chicago for body copy but uses something between AP and Chicago for headlines. Most magazines have a hybrid style derived from one of the two majors with custom carve-outs.
If you maintain a style guide for your own organization, the pragmatic approach is to pick AP or Chicago as your base and then explicitly document any deviations. A "we follow Chicago except we don't use the serial comma" rule is fine as long as it's written down so everyone applies it consistently.
Try it yourself
The fastest way to feel the difference is to take ten headlines you'd write at work and convert them under both styles in our case converter. Switch the style pill from AP to Chicago and watch which words flip. You'll quickly develop an intuition for which style produces output you find natural — and that intuition usually maps to the kind of writing you do day to day.