What do all possessive nouns contain?

All nouns used to show possession use an apostrophe.

• Singular possessives are formed by adding an apostrophe s ('s) to the end of a noun.
• For plural nouns that end in -s, the possessive are formed by adding an apostrophe after the existing -s ('); for irregular plural nouns that don't end with -s, the possessive is formed by adding the apostrophe s ('s), the same as a singular noun.