Web accessibility refers to the practice of making websites usable by people of all abilities and disabilities. When sites are correctly designed, developed and edited, all users can have equal access to information and functionality. For example, when a site is coded with semantically meaningful HTML, with textual equivalents provided for images and with links named meaningfully, this helps blind users using text-to-speech software and/or text-to-Braille hardware. When text and images are large and/or enlargable, it is easier for users with poor sight to read and understand the content. When links are underlined (or otherwise differentiated) as well as coloured, this ensures that color blind users will be able to notice them. When clickable links and areas are large, this helps users who cannot control a mouse with precision. When pages are coded so that users can navigate by means of the keyboard alone, or a single switch access device alone, this helps users who cannot use a mouse or even a standard keyboard. When videos are closed captioned or a sign language version is available, deaf and hard of hearing users can understand video. When flashing effects are avoided or made optional, users prone to seizures caused by these effects are not put at risk. And when content is written in plain language and illustrated with instructional diagrams and animations, users with dyslexia and learning difficulties are better able to understand the content. When sites are correctly built and maintained, all of these users can be accommodated while not impacting on the usability of the site for non-disabled users.
The needs that Web accessibility aims to address include:
- Visual: Visual impairments including blindness, various common types of low vision and poor eyesight, various types of color blindness;
- Motor/Mobility: e.g. difficulty or inability to use the hands, including tremors, muscle slowness, loss of fine muscle control, etc., due to conditions such as Parkinson's Disease, muscular dystrophy, cerebral palsy, stroke;
- Auditory: Deafness or hearing impairments, including individuals who are hard of hearing;
- Seizures: Photoepileptic seizures caused by visual strobe or flashing effects.
- Cognitive/Intellectual: Developmental disabilities, learning disabilities (dyslexia, dyscalculia, etc.), and cognitive disabilities of various origins, affecting memory, attention, developmental "maturity," problem-solving and logic skills, etc.;
Assistive technologies used for web browsing
Individuals living with a disability use assistive technologies such as the following to enable and assist web browsing:
- Screen reader software, which can read out, using synthesized speech, either selected elements of what is being displayed on the monitor (helpful for users with reading or learning difficulties), or which can read out everything that is happening on the computer (used by blind and vision impaired users).
- Braille terminals, consisting of a Refreshable Braille display which renders text as Braille characters (usually by means of raising pegs through holes in a flat surface) and either a QWERTY or Braille keyboard.
- Screen magnification software, which enlarges what is displayed on the computer monitor, making it easier to read for vision impaired users.
- Speech recognition software that can accept spoken commands to the computer, or turn dictation into grammatically correct text - useful for those who have difficulty using a mouse or a keyboard.
- Keyboard overlays, which can make typing easier and more accurate for those who have motor control difficulties.
Guidelines on accessible web design
Web Content Accessibility Guidelines
In 1999 the Web Accessibility Initiative, a project by the World Wide Web Consortium (W3C), published the Web Content Accessibility Guidelines WCAG 1.0. In recent years, these have been widely accepted as the definitive guidelines on how to create accessible websites.
Criticism of WAI guidelines
For a general criticism of the W3C process, read Putting the user at the heart of the W3C process. In articles such as WCAC 2.0: The new W3C guidelines evaluated, To Hell with WCAG 2.0 and Testability Costs Too Much, the WAI has been criticised for allowing WCAG 1.0 to get increasingly out of step with today's technologies and techniques for creating and consuming web content, for the slow pace of development of WCAG 2.0, for making the new guidelines difficult to navigate and understand, and other argued failings. In one attempt to provide guidelines that are designed to be up to date, easier to understand, and more relevant and practical to typical web development projects, Joe Clark's WCAG Samurai project has published an unofficial set of errata to WCAG 1.0.
Canada has the Common Look and Feel Standards requiring federal government internet websites to meet Web Content Accessibility Guidelines (WCAG) 1.0 Checkpoints Priorities 1 and 2 (Double A conformance level). The standards have existed since 2000 and were updated in 2007.
As part of the Web Accessibility Initiatives in the Philippines, the government through the National Council for the Welfare of Disabled Persons (NCWDP) board approved the recommendation of forming an adhoc or core group of webmasters that will help in the implementation of the Biwako Millennium Framework set by the UNESCAP.
The Philippines was also the place where the Interregional Seminar and Regional Demonstration Workshop on Accessible Information and Communications Technologies (ICT) to Persons with Disabilities was held where eleven countries from Asia - Pacific were represented. The Manila Accessible Information and Communications Technologies Design Recommendations was drafted and adopted in 2003.
In Spain, UNE 139803 is the norm entrusted to regulate the accessibility web.
In Sweden, Verva, the Swedish Administrative Development Agency is responsible for a set of guidelines for Swedish public sector web sites. Through the guidelines, Web accessibility is presented as an integral part of the overall development process and not as a separate issue.
The Swedish guidelines contain criteria which cover the entire lifecycle of a website; from its conception to the publication of live web content. These criteria address several areas which should be considered, including:
- web standards
- privacy issues
- information architecture
- developing content for the web
- Content Management Systems (CMS) / authoring tools selection.
- development of web content for mobile devices.
An English translation was released in April 2008: Swedish National Guidelines for Public Sector Websites
The translation is based on the latest version of Guidelines which was released in 2006.
Legally-required web accessibility
A growing number of countries around the world have introduced legislation which either directly addresses the need for websites and other forms of communication to be accessible to people with disabilities, or which addresses the more general requirement for people with disabilities not to be discriminated against.
In 2000, an Australian blind man won a court case against the Sydney Organising Committee of the Olympic Games (SOCOG). This was the first successful case under Disability Discrimination Act 1992 because SOCOG had failed to make their official website, Sydney Olympic Games, adequately accessible to blind users. The Human Rights and Equal Opportunity Commission (HREOC) also published World Wide Web Access: Disability Discrimination Act Advisory Notes. All Governments in Australia also have policies and guidelines that require accessible public websites; Vision Australia maintain a complete list of Australian web accessibility policies. 
In Ireland, the Disability Act 2005 was supplemented with the National Disability Authority's Code of Practice on Accessible Public Services in July 2006. It is a practical guide to help all Government Departments and nearly 500 public bodies to comply with their obligations under the Disability Act 2005.
In the UK, the Disability Discrimination Act 1995 (DDA) does not refer explicitly to website accessibility, but makes it illegal to discriminate against people with disabilities. The DDA applies to anyone providing a service; public, private and voluntary sectors. The Code of Practice: Rights of Access - Goods, Facilities, Services and Premises document  published by the government's Disability Rights Commission to accompany the Act does refer explicitly to websites as one of the "services to the public" which should be considered covered by the Act.
Website accessibility audits
A growing number of organizations, companies and consultants offer website accessibility audits. These audits, a type of system testing, identify accessibility problems that exist within a website, and provide advice and guidance on the steps that need to be taken to correct these problems.
A range of methods are used to audit websites for accessibility:
- Automated tools are available which can identify some of the problems that are present.
- Expert technical reviewers, knowledgeable in web design technologies and accessibility, can review a representative selection of pages and provide detailed feedback and advice based on their findings.
- User testing, usually overseen by technical experts, involves setting tasks for ordinary users to carry out on the website, and reviewing the problems these users encounter as they try to carry out the tasks.
Each of these methods has its strengths and weaknesses:
- Automated tools can process many pages in a relatively short length of time, but can only identify some of the accessibility problems that might be present in the website.
- Technical expert review will identify many of the problems that exist, but the process is time consuming, and many websites are too large to make it possible for a person to review every page.
- User testing combines elements of usability and accessibility testing, and is valuable for identifying problems that might otherwise be overlooked, but needs to be used knowledgeably to avoid the risk of basing design decisions on one user's preferences.
Ideally, a combination of methods should be used to assess the accessibility of a website.
- Computer accessibility
- Device Independence
- Multimodal interaction
- Progressive enhancement
- Web Interoperability
- Universal design
- UNE 139803
- "New Version of Guidelines for Swedish Public Sector Web Sites". Peter Krantz.
- Australian Web Accessibility Policies and Guidelines - AIS Resources - Accessible Information Solutions - Services - Vision Australia
- [http://www.equalityhumanrights.com/Documents/Disability/Accessibility_guidance/PAS78.pdf Equality and Human Rights Commission - Websites DDA Guidance
- Clark, Joe (2003). Building Accessible Websites. New Riders Press. ISBN 0-7357-1150-X.
- Thatcher, Jim (2003). Constructing Accessible Web Sites (Reprint ed.). Apress (Previously by Glasshaus). ISBN 1-59059-148-8. Unknown parameter
- Slatin, John (2002). Maximum Accessibility: Making Your Web Site More Usable for Everyone. Addison-Wesley Professional. ISBN 0-201-77422-4. Unknown parameter
- Paciello, Michael (2000). Web Accessibility for People with Disabilities. CMP Books. ISBN 1-929629-08-7.
- Bangeman, Eric (2006-09-10). "Judge: ADA lawsuit against Target can proceed". Ars Technica. Retrieved 2006-09-26. Check date values in:
Standards and guidelines
- The main page for the W3C's Web Accessibility Initiative (WAI)
- Wikipedia accessibility guidelines
- University of Illinois iCITA HTML Accessibility Best Practices
- New York State Mandatory Technology Standards for Accessibility of State Agency Web-Based Intranet and Internet Information and Applications – Fourteen standards derived from both U.S. Section 508 and the WAI's WCAG 1.0 and required for NYS agency web sites.
- Americans with Disabilities Act Section 508 Guidelines and Section 508 Homepage
- Unified Web Evaluation Methodology 1.2
- Equality and Human Rights Commission: PAS 78: a guide to good practice in commissioning accessible websites
- Disability Discrimination Act UK
- Section 508 - requires U.S. government web sites to be accessible
- New York State Technology Policy P04-002 – Requires Accessibility of State Agency Web-Based Intranet and Internet Information and Applications, requires all State entity web sites to be accessible according to NYS standards which are a hybrid of Section 508 and the W3C's WCAG 1.0. Updates Statewide Technology Policy 99-3, which required sites to conform to the W3C WCAG 1.0, Priority one checkpoints only.
- Disability Act 2005 Ireland
- Common Look and Feel Standards 2.0 Canada