This guide includes reference tools and educational resources related to materials that are freely available on the Internet and do not require subscription or registration on the part of individual researchers to access them. Most of these resources were created by educational institutions, scientific organizations, or are personal projects of materials scientists. A few commercial sites were included if they contained educational resources; however, sites were excluded if they were too much of a sales pitch for company products or services. Previous guides to web resources have become outdated and are filled by links to companies, professional societies, and government research agencies. I have chosen not to include such links in this guide, though many of the websites also happen to include a section of links to companies or societies.