The defining difference is how each handles prepositions. AP Style lowercases all prepositions, while Chicago Style only lowercases short prepositions of four letters or fewer.
AP Style title case capitalizes all major words while lowercasing articles, coordinating conjunctions, and all prepositions regardless of length. It is the standard of the Associated Press Stylebook.
AP Style is required by most American newspapers, digital news outlets, and press releases. Public relations professionals follow it because journalists expect it.
Open AP Style converterChicago Style capitalizes all major words and long prepositions while lowercasing short prepositions of four letters or fewer, articles, and coordinating conjunctions. It is the dominant style for American book publishing.
Chicago Style is required for most manuscripts submitted to book publishers, literary journals, and academic presses. Scholars in the humanities default to it.
Open Chicago Style converterAP Style is required by most American newspapers, digital news outlets, and press releases. Public relations professionals follow it because journalists expect it.
All prepositions are lowercased, whether short or long. This is the key rule that distinguishes AP Style from Chicago Style.
Chicago Style is required for most manuscripts submitted to book publishers, literary journals, and academic presses. Scholars in the humanities default to it.
Prepositions of five or more letters are capitalized. Short prepositions like in, on, at, by, and of remain lowercase.
Choose AP Style for journalism, press releases, and digital news content.
Choose Chicago Style for book manuscripts, academic papers, and literary publications.
A preposition like through or between is lowercase in AP Style but uppercase in Chicago Style. This single rule produces noticeably different results in titles with longer prepositions.