Some points of punctuation differ between American and British English, as explained by Grammar Girl Mignon Fogarty:
American English uses periods after abbreviations, including those formed by the first and last letter of the word (e.g., Dr. for doctor Mr. for mister) and those formed by the first letters of a word (e.g., alt. for altitude). British English drops the periods (Dr, Mr, alt).
American English places commas and periods INSIDE the quotation marks; British English places them outside. A common error by authors of scientific papers is to place periods and commas outside of quotes when using American English. See Grammarly.com for a nice review of guidance given by various style guides about punctuation with quotation marks.
Examples of the correct use of commas and periods with quotation marks in American English:
The experiment included 10 specimens designated as “aged” and 10 designated as “fresh.”
Theodore Roszak eloquently stated “Nature composes some of her loveliest poems for the microscope and the telescope,” and Rachel Carson wrote “In nature, nothing exists alone.”
In British English, the punctuation would look like this:
The experiment included 10 specimens designated as “aged” and 10 designated as “fresh”.
Theodore Roszak eloquently stated “Nature composes some of her loveliest poems for the microscope and the telescope”, and Rachel Carson wrote “In nature, nothing exists alone”.
Other marks, including colons, semicolons, question marks, and exclamation points that are not part of the quotation go outside the quotes in both language styles:
There was vigorous debate about Carl Sagan’s quote “In the vastness of the Cosmos there must be other civilizations far older and more advanced than ours″; however, few took issue with his musing that “The cosmos is within us…we are a way for the universe to know itself”!
How did the authors respond to the editor’s comment that “The specimens were not properly prepared”?
In both American and British English, when the punctuation is part of the quote itself, it is placed inside the quotation marks:
The questionnaire items included “How often were the specimens checked?” and “What factors were tested?”
Remember, in the U.S., periods and commas go inside the quotation marks. Outside the U.S., they go outside!
See our related post about British vs. U.S. spellings!