World Wide Web (Web) documents, once delivered in a form that remained constant whilst viewed, are now often dynamic, with sections of a page able to change independently, either automatically or as a result of user interaction. In order to make these updates, and hence their host pages, accessible, it is necessary to detect when the update occurs and how it has changed the page, before determining how, when and what to present to the user. This can only be achieved with an understanding of both the technologies used to achieve dynamic updates and the human factors influencing how people use them. After proposing a user-centred classification of dynamic updates, this paper surveys the current state of technology from two perspectives: that of the developer, and those of visually disabled users. For the former group, the paper introduces some of the technologies that are currently available for implementing dynamic Web pages, before reporting on the results of experiments analysing current and historical Web pages to determine the extent of use of these technologies `in the wild' and the trends in their uptake. The analysis shows that for the most popular 500 sites, JavaScript is used in 93%, Flash in 27% and about one-third (30%) use XMLHttpRequest, a technology used to generate dynamic updates. Uptake of XMLHttpRequest is approximately 2.3% per year across a random selection of 500 sites and is probably higher in the most popular sites. When examining dynamic updates from the perspective of visually disabled users, first an investigation is reported into which technologies (Web Browser and assistive technologies) are currently used by this group in the UK: Internet Explorer and JAWS are clear favourites. Then, the paper describes the results of an experiment, and supporting anecdotal evidence, which suggests that, at best, most users can currently reach updated content, but they must do so manually, and are rarely given any indication that any update has occurred. With technologies enabling dynamic updating of content currently deployed in about 30% of the most popular sites, and increasing annually, action is urgently required if visually disabled users are to be able to use the Web. The paper concludes by discussing some of the issues involved in making these updates accessible. ; 10.1007/s10209-011-0251-y