The Editor’s Manual
Free learning resource on English grammar, punctuation, usage, and style.
Use either a comma or a colon after a greeting. The colon is preferred in business or other formal communication in U.S. style.
Both a colon and an em dash introduce new information that explains or builds upon something that precedes it. The colon is quieter; the dash is more emphatic and dramatic.
Use a colon only after a grammatically complete sentence to introduce a list. Don’t use a colon between a verb and its object. Don’t use a colon after a title, heading, or caption for a list.
Don’t capitalize a word after a colon within a sentence, or a single sentence after a colon. Capitalize a question or a series of two or more sentences introduced by a colon. Also capitalize subtitles.
Use a colon to introduce a list or a quotation, or to explain and amplify a statement. It directs the reader’s attention to the information that follows. It can also serve as a sign or separator.