At Webdrips, we stress the importance of building accessible websites. The Drupal community also recognizes the importance of accessibility enough to have a pledge(link is external). And while many important modules and themes have taken the pledge, it's still extremely useful to know up-front how just how accessible your site needs to be. Obviously it's ideal to err on the side of caution and shoot for a WCAG2(link is external) rating of "AAA", but it may not always be possible when designing a site with excessive dynamic or animated content. As such, as part of the discovery phase of a new design or redesign, we will cover your audience in great detail.
If you're not sure how accessible your site is, we can help you make a quick determination, then work with you to develop a game plan to achieve the desired accessibility rating.
For a good overview on website accessibility, read Introduction to Web Accessibility