WCAG success criteria are divided into three levels of conformance: A, AA, and AAA. The levels are cumulative — AA includes all A criteria, and AAA includes all A and AA criteria. Understanding the difference is important because legal requirements and procurement standards consistently reference a specific level.
Level A — the floor
Level A criteria address the most critical barriers. If your site fails Level A, it will be unusable for some users with disabilities regardless of the assistive technology they use. Examples include providing text alternatives for images, ensuring keyboard accessibility for all functionality, and not using color as the only way to convey information. Level A alone is not considered sufficient for compliance.
Level AA — the standard
Level AA is the practical compliance target. It builds on Level A with criteria around color contrast (4.5:1 for normal text), resize text, input labels, consistent navigation, and more. This is the level cited by the ADA, Section 508, and the EU Accessibility Act. Most legal settlements and procurement requirements specify WCAG 2.1 or 2.2 Level AA.
Level AAA — aspirational
Level AAA contains the most stringent criteria. The W3C explicitly notes that it is not possible to satisfy all Level AAA criteria for all content. Examples include sign language interpretation for audio, 7:1 contrast for text, and no timing on interactions. Organizations should adopt individual AAA criteria where feasible, but AAA conformance is not a realistic blanket target.
Tip
When a legal document or contract says "WCAG compliant," it almost always means WCAG 2.1 or 2.2 Level AA. If the level is unspecified, treat it as AA.
Conformance vs. best effort
Full WCAG conformance means all content on all pages meets every success criterion at the stated level. In practice, most organizations declare partial conformance or document known exceptions in an Accessibility Statement. What matters is having a documented, improving posture — not claiming perfection you cannot support.