Quotation marks are used to set off speech or quoted sentences and words. Despite its simple role, people tend to get confused about the position of other punctuation in relation to the quotation marks. Should it go inside or outside the quotation marks?
It depends. If you are writing in American English, other punctuation should go inside the quotation marks, even if it is not part of the quoted sentence. Here is an example from the New York Times:
“When we have got a contractor city, say, of 180,000 people, and there hasn’t been a completed prosecution of anybody coming out of Iraq, not one,” he said, “what sort of city in America would be like that, where no one is prosecuted for anything for three years? It’s unthinkable.”
If you are writing in British English, on the other hand, punctuation that is not part of the quoted sentence should be place outside the quotation marks. Here is an example from The Telegraph:
A crisis in the US subprime mortgage market will affect Britain, he said, warning that the housing market is likely to weaken as a result. However, he insisted that the economy is starting from “a very strong position”.
Notice that colons and semicolons are always placed outside the quotation marks, and that you should not finish a sentence with more than one punctuation mark, regardless of the rule you are using.