Web Content Accessibility Guidelines (WCAG) are web accessibility guidelines developed as part of the Web Accessibility Initiative (WAI) by the World Wide Web Consortium (W3C). The guidelines are internationally recognized as best practice worldwide.
WCAG focus on four main principles:
Within each of these four areas, there is a set of guidelines, and each guideline has a set of success criteria.
The individual success criteria are most commonly used for conformance requirements. They are divided into three levels: level A, level AA and level AAA. Most organizations are required to conform with level AA (all criteria on level A and level AA).
For further information see "Web Content Accessibility Guidelines (WCAG) Overview" from the World Wide Web Consortium (W3C).