This is a question that is constantly getting me in hot water with my composition teachers. The answer is a simple one. It’s just that my teachers don’t like the answer I choose. It’s all right, though my choice of placement has gotten me a few squiggly red marks on my papers, it hasn’t yet cost me my “A”.
American usage demands that all punctuation go inside the quote mark, end of story, no argument allowed.
British usage allows for a little common sense and asks, what is being quoted? If the punctuation is part of what is being quoted, then the punctuation goes inside of the quote mark. However, if the punctuation is part of the larger sentence, and the quote just happens to be at the end of it, then the punctuation goes on the outside of the quote mark.
John Doe of ACME Pharmaceuticals said, “We are not releasing any waste materials into the river.” What John said is a complete sentence that ends with a period, so the period goes on the inside of the quote marks, since you are quoting the entire sentence.
According to John Doe of ACME Pharmaceuticals, the company is “not releasing any waste”. The words “not releasing any waste” are a direct quote, so they belong inside quotations marks, however they are not a full sentence, and they are not the end of the sentence John said, so the period does not belong on the inside of the quotation marks. However, they are at the end of the sentence I wrote about what John said, so the period belongs at the end of my sentence.