All international accessibility standards are aimed at increasing accessibility in broad and specific contexts. So, it is not surprising that while there are differences among the standards, they all have similar underlying principles. Focusing on the Web Content Accessibility Guidelines (WCAG), there are four underlying principles.

WCAG Principles

The acronym for the four WCAG principles is POUR:

  • Perceivable: Information and user interface components must be presented to users in ways they can perceive. Perception, in this case, goes beyond sight and includes considering other ways people can recognize and use your content (e.g., audio cues).
  • Operable: User interface components and navigation must be operable by a broad audience. Not everyone uses a keyboard and mouse, and many devices require touch technology. Assistive technologies, such as screen readers, enable users to interact with your content in a way that works for them.
  • Understandable: All aspects of your content, from the information itself to the operation of the functional user interface, must be easy to understand. Clear labels and recognizable design patterns reduce the effort in learning how to use and interact with your content.
  • Robust: Content must be established and reliable enough to be interpreted consistently by as many browsers and assistive technologies as possible. A robust application is stable and future friendly.

Other international standards (such as ETSI 301 549) incorporate WCAG standards and add additional principles and consideration that are applicable to software and hardware, or other information and communications technology.

WCAG Versions and Levels

Three levels prioritize the success criteria, Levels A, AA and AAA:

  • Level A is the lowest level required to meet success criteria. Applications meeting Level A conformance alone are not accessible. However, these are the most important success criteria to achieve.
  • Double A (AA) includes Level A criteria. To be AA conformant, you would need to exceed Level A and meet Double A techniques. These are the second most important criteria.
  • Triple A (AAA) A is the highest use of WCAG success criteria. Meeting AAA can be challenging and sometimes impossible for some technologies.


It’s common to aim for Level AA conformance, because this provides a good level of accessibility, and it’s normally achievable with most content. It is also reflective of AODA website standards.

Remember, meeting all Website Accessibility Guideline Success Criteria does not necessarily make your product accessible.



Icon for the Creative Commons Attribution 4.0 International License

eCampusOntario's Digital Accessibility Toolkit Copyright © by eCampus Ontario is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

Share This Book