Use apostrophes to form the possessive case of nouns and indefinite pronouns, and contractions. Optionally, apostrophes may also be used in the plurals of abbreviations and numbers.
Form the possessive of singular nouns and indefinite pronouns and of plural nouns that do not end in -s by adding -'s.
bacterium's [The plural is
children's [The singular is
Also form the possessive of singular nouns that end in -s by adding -'s.
Form the possessive of plural animate nouns that end in -s by adding only the apostrophe after the -s:
Try to form the possessive of inanimate nouns by using the preposition of.
composition of microchips
position of the planets
Optionally, use the apostrophe to form the plurals of acronyms and numbers. Be consistent, however, throughout a document. Always use the apostrophe to form the plurals of lowercase letters.
R.E.M's or REM's or REMs
386's or 386s
Use the apostrophe to form standard contractions of certain words.
it + is = it's
we + will = we'll