Result
Not when it is a preposition, which is how it appears in most titles ("Love in the Time of Cholera"). All six major guides keep two-letter prepositions lowercase mid-title. When "in" finishes a verb instead, as in "Log In" or "Check In," it works as an adverb and gets a capital.
"In" by Style Guide
| Style guide | "In" mid-title | Why |
|---|---|---|
| AP | Lowercase | Prepositions of three or fewer letters stay lowercase |
| APA | Lowercase | Short prepositions (three or fewer letters) stay lowercase |
| Chicago | Lowercase | Prepositions are lowercase at any length |
| MLA | Lowercase | Prepositions are lowercase at any length |
| AMA | Lowercase | Prepositions of three or fewer letters stay lowercase |
| Bluebook | Lowercase | Prepositions of four or fewer letters stay lowercase |
Examples in Chicago Style
- Life in the City
- A Week in Paris
- What's New in Title Case
- Trouble in Paradise
When "In" Is Capitalized
- Phrasal verbs: "How to Log In," "Why You Should Check In Early," "Giving In." No noun follows "in," so it is an adverb, and Chicago states that such words are capitalized.
- First word: "In Cold Blood."
- First word of a subtitle: "Remote Teams: In Practice."
- Last word: AP, Chicago, and MLA capitalize any final word ("Let the Light In").
Hyphenated compounds that start with "in" capitalize it as the first element: "In-Depth," "In-House." See the hyphenated word rules.
Related Words
"Into" has four letters, so AP, APA, and AMA capitalize it while Chicago, MLA, and Bluebook do not. "On" and "at" follow the same rules as "in."
Real Titles With "In"
- In Cold Blood (Truman Capote): first word
- Alice's Adventures in Wonderland (Lewis Carroll): lowercase mid-title
- Love in the Time of Cholera (Gabriel García Márquez): lowercase mid-title
"In" 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 "in" is lowercase unless it starts the title: "Life in the city." Pick one of the two styles for a whole set of headings rather than mixing them.
Quick Answers
Should "in" be capitalized in a title?
Not as a preposition. Every major guide lowercases "in" mid-title unless it works as an adverb, as in "Log In."
Is "in" capitalized in APA?
No. APA lowercases prepositions of three letters or fewer.
Is "in" capitalized in "Sign In"?
Yes. There "in" completes the verb and has no object, so it is an adverb.