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.
Capital Community College Foundation
Guide to Grammar and Writing: The Apostrophe
What is an apostrophe? Where are apostrophes found in writing? Use this website to learn more about these crazy little punctuation marks.
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.