Capitalization style guide

This guide is a summarized quotes from Chicago Manual of Style 16th ed.

Capitalizing title

(rule 8.165)

• Capital lower case or in caps and small caps
• Use either sentence style or headline style

Sentence style

(rule 8.166)

• Only the first word in a title, the first word in a subtitle, and any proper names

Headline style

(rule 8.167)
These are pragmatic rather than logical

1. Capitalize the first and last words both in title and in subtitles and all other major words (nouns, pronouns, verbs, adjectives, adverbs, and some conjunction—see rule 4)
2. Lowercase the articles the, a, and an.
3. Lowercase prepositions, regardless of length, exept when they are stressed (through in A River Runs Through It), are used adverbially or adjectivaly (up in Look Up, down in Turn Down, on in The On Button, etc.), are used as conjunctions (before in Look Before You Leap, etc.), or are part of a Latin expression used adjectivally or adverbially (De Facto, In Vitro, etc.).
4. Lowercase the conjunctions and, but, for or nor.
5. Lowercase the words to and as in any grammatical function, for simplicity's sake.
6. Lowercase the second part of a species name, such as lucius in Esox lucius, or the part of a proper name that would be lowercased in text, such as de or von.

…
If you are not sure what grammatical function a word is performing (or even if you are), try reading the title aloud: if you would stress the word, capitalize it; if not, lowercase it.

Capitalizing hyphenation

(rule 8.169-8.170)
Simple rule: capitalize only the first element unless any subsequent element is a proper noun or adjective

Traditional rules: (more complex, preferred by Chicago)

1. Always capitalize the first element.
2. Capitalize any subsequent elements unless they are articles, prepositions, coordinating conjunctions (and, but, for, or, nor) or such modifiers as flat or sharp following musical key symbols.
3. If the first element is merely a prefix or combining form that could not stand by itself as a word (anti, pre, etc.), do not capitalize the second element unless it is a proper noun or proper adjective.
4. Do not capitalize the second element in a hyphenated spelled-out number (twenty-one, etc.).
5. Break a rule when it doesn't work, e.g., Run-ins and Take-offs (lowercase short and unstressed elements)

Rules to be confirmed:

• Captialization after colon: you’re supposed to capitalize after the colon when the colon introduces (1) a quotation or (2) multiple sentences. (source: CMS_FAQ)

Application & Web

• Textmate have a menu Text -> Convert -> To Titlecase which works well with the guideline above except that you should lowercase "a" in "as" and "o" in "Twenty-one". (See rules above.)
• I always use this web service. However, I don't know which rules it follows. (Thomas)