The Web is the most pervasive collaborative technology in widespread use today; however, access to the Web and its many applications cannot be taken for granted. Web accessibility encompasses a variety of concerns ranging from societal, political, and economic to individual, physical, and intellectual through to the purely technical. Thus, there are many perspectives from which Web accessibility can be understood and evaluated. In order to discuss these concerns and to gain a better understanding of Web accessibility, an accessibility framework is proposed, using as its base a layered evaluation framework from computer supported co-operative work research and the ISO standard ISO/IEC 9126 on software quality. The former is employed in recognition of the collaborative nature of the Web and its importance in facilitating communication. The latter is employed to refine and extend the technical issues and to highlight the need for considering accessibility from the viewpoint of the Web developer and maintainer as well as the Web user. A technically inaccessible Web is unlikely to be evolved over time. A final goal of the accessibility framework is to provide Web developers and maintainers with a practical basis for considering Web accessibility through the development of a set of accessibility factors associated with each identified layer.