The Editor's Manual
Free learning resource on English grammar, punctuation, usage, and style.
Round brackets are called “parentheses” in American English but referred to simply as “brackets” in British English. In American writing, square brackets are used within parentheses, while the British use round within round brackets (nested parentheses).
Use commas to integrate closely related information into the flow of the sentence. Use parentheses to set off supplementary information or an afterthought from surrounding text. Use dashes to be emphatic or dramatic and make additional information or an aside stand out.
Place punctuation inside parentheses if it belongs to the parenthetical text, and outside if it belongs to the larger sentence. Periods, question marks, exclamation points, and quotation marks go inside if they are meant to punctuate the parenthetical text, while commas, dashes, colons, and semicolons always appear after a closing parenthesis.
Place a period within parentheses if the entire sentence is contained in the parentheses. Place the period outside if the parenthetical phrase appears within a larger sentence.
Parentheses (round brackets) are the most commonly used brackets in English, followed by square brackets. The other two types of brackets are braces and angle brackets. Each type serves a different purpose.
Parentheses set off information that may be useful but is tangential to the primary meaning of the passage. Square brackets enclose editorial clarifications to quoted text. Square brackets are also used as brackets within brackets.
Use square brackets within parentheses to show brackets within brackets. In British style, round brackets are used within round brackets. Avoid using nested parentheses in U.S. writing.
Use parentheses (or round brackets) to set off supplementary information from surrounding text. Such information should not be essential to the grammar of the sentence. Periods go within parentheses if they belong to the parenthetical matter but outside otherwise.