WAI Accessibility Guidelines

W3C Web Accessibility Initiative (WAI) develops and maintains:

• WCAG - Web Content Accessibility Guidelines
  http://www.w3.org/WAI/intro/wcag
• ATAG - Authoring Tool Accessibility Guidelines
  http://www.w3.org/WAI/intro/atag
• UAAG - User Agent Accessibility Guidelines
  http://www.w3.org/WAI/intro/uaag

Also: WAI-ARIA for accessible web applications.