Parentheses () | Definition, Punctuation, Rules & Examples

Parentheses are used to add extra information in a sentence. In academic writing, they are most often used to convey technical information such as equations, to introduce acronyms, and for parenthetical citations.

Side-by-side parentheses

Sometimes you might need to use two parenthetical elements together – for example, when a sentence contains both an acronym and a citation. Style guides disagree about whether it’s okay to place two (or more) parenthetical asides side by side.

APA style recommends using a single set of parentheses with a semicolon separating the main elements.

  • The results were sorted by gross domestic product (GDP; Odin, 2018).

Chicago also advises this approach, but allows side-by-side parentheses if their content is entirely unrelated. If you do use two sets of parentheses, put a space between them.

Nested parentheses

When you want to enclose a set of parentheses inside another set, most style guides recommend using square brackets for the inner element.

  • Several prestigious organizations (e.g., National Institutes of Health (NIH)) supported the initiative.
  • Several prestigious organizations (e.g., National Institutes of Health [NIH]) supported the initiative.

In British English, parentheses within parentheses are more acceptable. However, it’s always best to avoid this kind of nesting whenever possible. If you can rephrase the sentence to remove one of the parenthetical elements, this is the best option.

  • Several prestigious organizations, such as the National Institutes of Health (NIH), supported the initiative.

When including a citation within a parenthetical element, APA style recommends using commas instead of parentheses or brackets.

  • This sort of testing is usually unreliable (as Jenner [2012] took pains to show).
  • This sort of testing is usually unreliable (as Jenner, 2012, took pains to show).

Sources in this article

We strongly encourage students to use sources in their work. You can cite our article (APA Style) or take a deep dive into the articles below.

This Scribbr article

Bryson, S. (2022, October 10). Parentheses () | Definition, Punctuation, Rules & Examples. Scribbr. Retrieved November 13, 2022, from


Butterfield, J. (Ed.). (2015). Fowler’s dictionary of modern English usage (4th ed.). Oxford University Press.

Garner, B. A. (2016). Garner’s modern English usage (4th ed.). Oxford University Press.

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Shane Bryson

Shane finished his master's degree in English literature in 2013 and has been working as a writing tutor and editor since 2009. He began proofreading and editing essays with Scribbr in early summer, 2014.