Punctuation Guide

The following list provides guidance on the most commonly used and misused punctuation marks.

Ampersand (&)
  • in bibliographies: Use "&" or "and" in publishers’ names, regardless of how the publisher uses it on the title page—but be consistent
  • in book titles: Spell out and when listing a book title, regardless of how the original title was rendered
  • in course names: Spell out in course names (e.g., Intermediate Algebra and Trigonometry)
  • in parenthetical references, footnotes, and bibliographies: Use “&” (Johnson & Johnson)
  • in text: Spell out “and”

Apostrophe (')

Add an apostrophe and an "s" to most singular nouns to form the possessive, and only an apostrophe for plural nouns (except for a few irregular plurals that no not end in s). If the noun ends in s, x, or z add an apostrophe and an "s" (Chicago 7.17–7.18).

An apostrophe is never used to form the plural.

It is used to avoid confusion in plural nouns that are lowercased or are abbreviations (Chicago 7.14).

  • The Rockville Campus’s building (singular noun ending in s)
  • the Williamses’ new house, but the Joneses (forming a plural, no apostrophe needed)
  • FDR’s legacy
  • 2010’s heaviest snowstorm
  • MA’s and PhD’s
  • the three Rs, the 1900s, threes and fours (forming a plural, no apostrophe needed)

Straight versus slanted apostrophes

For printed material, the typographer’s mark (“smart quotes”) is preferable to the straight one, which is more prevalent in Internet material and other software applications. MS Word automatically generates the preferred quotation mark.

Artwork (see also, Quotes, Italics, or Nothing?)

Italicize titles of paintings, drawings, and statues.

  • Grant Wood’s American Gothic; Rodin’s Thinker

Books and periodicals (see also, Quotes, Italics, or Nothing?)

Italicize titles of books and periodicals.

  • For Whom the Bell Toll, Newsweek, The Washington Post
  • campus’s (singular possessive), campuses’ (plural possessive) (Chicago 7.15)

Comma (,)

Commas in city and state names: Enclose states, provinces, and territories in commas to set it from the rest of the sentence. (Chicago 6.17)

  • The committee will meet at the Rockville, Maryland, location.

Comma in Dates: In text, insert commas after the date and the year.

  • He was born on July 11, 1955, in Eugene, Oregon. (Chicago 6.45)
  • The event will be held on July 11. (not 11th or 11th)

Comma in Proper Names: “Jr.” is no longer set off by commas; neither is a numeral suffix.

  • Alan Miller Jr. works at the College; but Henry James II does not (Chicago 6.47)

Comma in Numbers: Insert a comma in numbers of more than three digits.

  • 1,000; $2,580

Comma in a Series: In lists of three or more items, use a comma before the word “and” and “or.”

  • They will serve breakfast, lunch, and dinner. (Chicago 6.18)

Dash (and hyphen)

In typesetting, three distinct symbols are used: hyphen (-), dash (–) also called an en dash, and em dash (—).

Em dash: Use an em dash (made up of two hyphens) or parentheses to set off a full phrase when the phrase contains a series of words that must be separated by commas. Also, use an em dash to denote an abrupt change in thought in a sentence or an emphatic pause.

  • We will fly to San Diego in June—if the travel expense is approved.

En dash: Use an en dash (half the size of an em dash) to indicate a range.

  • 1992–1993
  • pages 12–105
  • 10 a.m.–5:30 p.m.
  • Monday–Friday

Hyphen: Use a hyphen in phone numbers and all fractions.

  • 240-567-7000
  • one-third, three-fifths 


For titles of movies, television, radio programs, plays, works of art (paintings, drawings, statues), books, and periodicals, use italics.

  • One Flew Over the Cuckoo’s Nest (movie)
  • The Sopranos (TV)
  • WAMU’s Drive Time (radio show)
  • Sweeney Todd (play)
  • Rodin’s Thinker and Grant Wood’s American Gothic (artwork)
  • A Farewell to Arms (book)
  • The Washington Post, Newsweek (periodicals)


Do not hyphenate words beginning with pre, except: pre-dentistry, pre-engineering, pre-medicine, pre-medical technology, pre-optometry, pre-pharmacy, and similar words.


Do not hyphenate prefixes, generally, but hyphenate when the adjacent letters are duplicated, or the prefix stands alone and when necessary to avoid confusion with other words. When in doubt, it is never wrong to keep a hyphen to avoid misleading or puzzling forms (e.g., re-cover versus recover, un-ionized versus unionized). See also, Chicago 7.85 for “Hyphenation guide for compounds and words formed with prefixes.”

  • semi-independent, ultra- and subsonic vibrations
  • non-native, anti-intellectual 

Note: When the second element consists of more than one word, use an en dash, not a hyphen: pre–World War I. (Chicago 6.80)