English Plus+
Grammar Slammer's Apostrophes Showing Possession
This site discusses the correct and incorrect usage of apostrophes to show possession and examples are provided. Note that links are provided at the bottom of the page for other specific uses of the apostrophe.
SUNY Empire State College
Empire State College: Apostrophes
This resource looks at the three main uses of apostrophes: to take the place of deleted letters; to show possession; and to show plurals of letters, numbers, symbols, abbreviations and words used as words.
Language Guide
Language Guide: La Posesion
A basic explanation of pronouns used to show possession. Examples are interactive audio files for modeling correct pronunciation. A link to a practice quiz is provided.
Online Writing Lab at Purdue University
Purdue University Owl: Possessive Pronoun and Apostrophe
This Purdue Online Writing Lab article explains the three uses of the apostrophe.