Headlines and Titles of Works
Q. Should the first letter of all words in the title of a book, movie, or play be capped? I’ve sometimes seen the first letter of prepositions and articles in lowercase.
A. Although computer automation favors capping all the words in a title because it’s easy to do, traditionally only the important words (and not prepositions) are capped. There are exceptions; CMOS lays them out in its section on headline style.