Title Case Rules Explained: AP, Chicago, and What to Capitalize
Title case looks simple until you have to do it correctly. Most people capitalize the first letter of every word and call it done — but that is not real title case, and it looks wrong to anyone who edits professionally. True title case follows rules about which words get capitalized and which stay lowercase, and those rules differ slightly between style guides. Here is how it actually works.
The basic rule
In standard title case, you capitalize the first and last words of the title no matter what, plus all the principal words in between — nouns, pronouns, verbs, adjectives, and adverbs. You leave lowercase the small connecting words: short articles (a, an, the), short coordinating conjunctions (and, but, or, nor), and short prepositions (in, on, of, to, at, by). So "the lord of the rings" becomes "The Lord of the Rings" — "the" and "of" stay lowercase in the middle, but "The" is capitalized because it starts the title.
The words that stay lowercase
The lowercase words fall into three groups. Articles: a, an, the. Coordinating conjunctions: and, but, or, nor, for, so, yet. And short prepositions: of, to, in, on, at, by, up, for, off, and similar. The key word is short. When a preposition gets longer — "between," "through," "against" — most style guides capitalize it. And any of these words gets capitalized if it is the first or last word of the title, regardless of the rule.
AP style vs Chicago style
The two most common American style guides differ on the details. Associated Press (AP) style, used by journalists, capitalizes all words of four letters or more, which means it capitalizes longer prepositions like "With," "From," and "Into." Chicago style, used in publishing, focuses on the part of speech rather than length — it lowercases all prepositions regardless of length unless they are used as another part of speech. So AP would write "Walking Into the Room" while Chicago would write "Walking into the Room." Neither is more correct; they are different conventions for different fields.
The verb 'to be' trap
A classic mistake is lowercasing "is," "are," "be," and "was" because they are short. But these are verbs, and verbs are always capitalized in title case no matter how short. So it is "The Sky Is Blue," not "The Sky is Blue." The same applies to short pronouns like "It" and "He" — short, but capitalized because of what they are. Length alone does not decide capitalization; part of speech does.
Other cases worth knowing
Beyond title case, a few other conventions come up. Sentence case capitalizes only the first word and any proper nouns, like a normal sentence — increasingly popular for headlines and UI text because it reads as less shouty. ALL CAPS is used for emphasis but is harder to read in long stretches and can read as shouting. And small caps and other styles exist for specific design contexts. Knowing which case a context expects saves you from looking careless.
Doing it quickly
Applying title case by hand to a long list of headings is tedious and error-prone. A case converter gives you a clean starting point — capitalizing each word — which you can then fine-tune by lowercasing the specific articles and prepositions your chosen style guide requires. For sentence case, all caps, or lowercase, the conversion is exact and instant, which is especially handy for fixing text that arrived in the wrong case.