Result
It depends on the style guide. "Under" is a five-letter preposition. AP, APA, AMA, and Bluebook capitalize prepositions of that length, so they write "Under." Chicago and MLA lowercase prepositions no matter how long they are, so "under" stays lowercase there unless it is the first or last word.
"Under" by Style Guide
| Style guide | "Under" mid-title | Why |
|---|---|---|
| AP | Capitalize | Prepositions of four or more letters are capitalized |
| APA | Capitalize | Words of four or more letters are capitalized |
| Chicago | Lowercase | Prepositions are lowercase at any length |
| MLA | Lowercase | Prepositions are lowercase at any length |
| AMA | Capitalize | Prepositions longer than three letters are capitalized |
| Bluebook | Capitalize | Prepositions longer than four letters are capitalized ("under" has five) |
"Under" is long enough to clear even Bluebook's cutoff, which lowercases prepositions only up to four letters. That puts it in the same group as "about", "after", and "among".
The Same Headline in Four Styles
| Style | "life under the sea" |
|---|---|
| AP | Life Under the Sea |
| APA | Life Under the Sea |
| Chicago | Life under the Sea |
| MLA | Life under the Sea |
| Style | "cooking under pressure" |
|---|---|
| AP | Cooking Under Pressure |
| APA | Cooking Under Pressure |
| Chicago | Cooking under Pressure |
| MLA | Cooking under Pressure |
When Chicago Capitalizes "Under"
Chicago lowercases "under" only when it is a preposition, meaning a noun follows it ("under the bridge"). When it works as an adverb, it is capitalized: "Going Under" or "How the Company Went Under." It is also capitalized as the first word ("Under the Dome") and as the last word in AP, Chicago, and MLA.
Compounds With "Under"
Closed compounds such as "underwater," "underground," and "understand" are ordinary words, so every guide capitalizes them: "Life Underwater." Hyphenated forms like "Under-the-Radar" follow the hyphenated word rules, where each part is judged on its own.
Related Words
Its opposite, "over", has four letters, so it splits the guides differently: AP, APA, and AMA capitalize it, while Chicago, MLA, and Bluebook lowercase it.
Real Titles With "Under"
- Under the Dome (Stephen King): first word
- Under the Tuscan Sun (Frances Mayes): first word
"Under" in Sentence Case
APA reference lists, many news sites, and most UI text use sentence case instead of title case. There, only the first word and proper nouns get capitals, so "under" is lowercase unless it starts the title: "Life under the sea." Pick one of the two styles for a whole set of headings rather than mixing them.
Quick Answers
Should "under" be capitalized in a title?
In AP, APA, AMA, and Bluebook, yes. In Chicago and MLA, no, unless it is used as an adverb or sits first or last.
Is "under" capitalized in APA?
Yes. "Under" has five letters, and APA capitalizes every word of four letters or more.
Is "under" capitalized in Chicago style?
Not as a preposition. Chicago lowercases prepositions at any length but capitalizes adverb uses like "Going Under."