This is an international organization that leads the development of Web standards. The World Wide Web Consortium (W3C) Web Accessibility Initiative (WAI) was launched to promote Web functionality for people with disabilities.
WebAIM is an initiative from Utah State University. This organization’s Web site has great information about Web accessibility, including a tutorial. Also, this is the organization that created WAVE (Web Accessibility EValuation tool). You can use this Web-based tool to determine whether your Web site is accessible.