The Web is an increasingly important resource in many aspects of life: education, employment, government, commerce, health care, recreation, and more. It is essential that the Web be accessible in order to provide equal access and equal opportunity to people with disabilities. Web accessibility means that people with disabilities can use the Web, it means that they can perceive, understand, navigate, and interact with the Web, and that they can contribute to the Web. It encompasses all disabilities that affect access to the Web, including visual, auditory, physical, speech, cognitive, and neurological disabilities.

Web accessibility also benefits people without disabilities. For example, a key principle of Web accessibility is designing Web sites and software that are flexible to meet different user needs, preferences, and situations. This flexibility also benefits people without disabilities in certain situations, such as people using a slow Internet connection, people with "temporary disabilities" such as a broken arm, and people with changing abilities due to aging.

The Web Content Accessibility Guidelines 2.0 are organized into three levels of conformance:

• Level A – the most basic web accessibility features.
• Level AA – deals with the biggest and most common barriers for disabled users.
• Level AAA – the highest level of web accessibility, that many websites cannot reach.

For most websites, Level AA plus some Level AAA is the best target. That’s because some of the highest level guidelines simply can’t be applied to all websites.

Starting with Level A is a great way to make progress and begin helping out your users. Level AA is the standard many governments are using as a benchmark as this targets the most common and most problematic issues for web users

In the 2018, WCAG 2.0 updated to version 2.1 with new guidelines for making websites even more accessible.
The new guidelines in WCAG 2.1 is backward compatible with WCAG 2.0. This means that:

• The previous categories and guidelines still apply
• The numbering still applies
• The basic principles still apply
• The three levels of success criteria (A, AA, AAA) still apply

The main goal is to make websites more usable for people with visual and cognitive disabilities