The web application is increasingly a platform of choice for complex business software, as well as for Internet online services. We are beginning to identify guidelines for web application architectures that support accessibility. This paper describes common accessibility problems encountered in web applications and explains how architecture can help address these problems through reusable accessible objects; supplementing information in links, buttons and labels; providing comparable access to signposting; handling errors; and providing timeout notification and recovery. It also discusses the critical role of architecture in supporting what we believe is the best way of meeting the needs of diverse user groups: multiple dynamic views of the user interface.