When do you put punctuation in quotation marks?

A period is always placed inside quotes, it is never put outside of quotes. "This is incorrect". "It should be written like so." "It should also not do this. "

The reason for the convention is actually a mechanical, printing issue. In the old days of manual typeset, a period after the quotes was vulnerable to falling off or being cut off because the period was off to the side.

Interestingly, the British convention is the opposite -- the period is outside of quotes.

Comment

No, British English is not 'the opposite' to the American system regarding the position of the period (full stop). In British English, the placement of the period depends upon the structure of the sentence and is more logical -if it applies to the quote, then it's within the quotation marks; if it applies to the sentence that contains the quote, then it is placed outsidethe quotation marks.

For example: # "The horse was black." (inside quotation marks) # George said that the "horse was black". (outside quotation marks)

In the first case, the period applies to the quotation. In the second case, the period applies to the sentence that contains the quotation.