Two words brought together as a compound may be written separately, written as one word, or connected by hyphens. For example, three modern dictionaries all have the same listings for the following compounds:

Another modern dictionary, however, lists hairstylist, not hair stylist. Compounding is obviously in a state of flux, and authorities do not always agree in all cases, but the uses of the hyphen offered here are generally agreed upon.

1. Use a hyphen to join two or more words serving as a single adjective before a noun:
   a one-way street
   chocolate-covered peanuts
   well-known author
   However, when compound modifiers come after a noun, they are not hyphenated:
   The peanuts were chocolate covered.
   The author was well known.
2. Use a hyphen with compound numbers:
   forty-six
   sixty-three
   Our much-loved teacher was sixty-three years old.
3. Use a hyphen to avoid confusion or an awkward combination of letters:
   re-sign a petition (vs. resign from a job)
   semi-independent (but semiconscious)
   shell-like (but childlike)
4. Use a hyphen with the prefixes ex- (meaning former), self-, all-; with the suffix -elect; between a prefix and a capitalized word; and with figures or letters:
   ex-husband
   self-assured
   mid-September
   all-inclusive
   mayor-elect
   anti-American
   T-shirt
   pre-Civil War
   mid-1980s
5. Use a hyphen to divide words at the end of a line if necessary, and make the break only between syllables:
   pref-er-ence
   sell-ing
   in-di-vid-u-al-ist
6. For line breaks, divide already-hyphenated words only at the hyphen:
   mass-
   produced
   self-
   conscious
7. For line breaks in words ending in -ing, if a single final consonant in the root word is doubled before the suffix, hyphenate between the consonants; otherwise, hyphenate at the suffix itself:
   plan-ning
   run-ning
   driv-ing
   call-ing
8. Never put the first or last letter of a word at the end or beginning of a line, and don't put two-letter suffixes at the beginning of a new line:
   lovely (Do not separate in a way which leaves ly beginning a new line.)
   eval-u-ate (Separate only on either side of the u; do not leave the initial e- at the end of a line.)