Put an opening double quotation mark where you begin to borrow another person’s exact words, and put a closing double quotation mark where you stop borrowing, whether the quotation is a complete sentence or only part of one:

For a fuller discussion of attributing and punctuating quotations, see Chapter 19.

Use single quotation marks only to set off a quotation within a quotation.

One blogger wrote, “To me, ‘If not now, when?’ is the essential question.”