Do you capitalize the word "in" or "on" in book titles?

For example, if there was a book called "He Is in the Park", would you capitalize the word "in"?

Thanks,
Leo

Not usually. See Rule 8:

http://www.grammarbook.com/punctuation/capital.asp

No, you would not. Just as you don't capitalize the of in United States of America

In book titles, it is generally customary to capitalize most words, including nouns, verbs, adjectives, adverbs, and pronouns. However, smaller words like articles (e.g., "a," "an," "the"), prepositions (e.g., "in," "on," "at"), and conjunctions (e.g., "and," "but," "or") are typically not capitalized, unless they are the first or last word of the title.

In the specific example you provided, "He Is in the Park," the word "in" is a preposition and would not be capitalized in most style guides. However, it is important to note that style preferences can vary, and some authors, publishers, or style guides might choose to capitalize all words in a title. Thus, it is always a good idea to consult the specific style guide or follow any guidelines provided by the publisher you are working with.