We present 19 systems that have been developed over the past decade to support collaborative writing over the Web. The aim of this article is to present the state of the art on the use of the Web for collaborative writing and thus (1) help designers improve current systems or define future systems, and (2) help users choose the most appropriate system to support their needs. Among available systems, groups can select from tools to write a document (on- or off-line), collect comments about a document, or maintain a Web site. The lack of experimental data concerning Web-based applications forces designers to use other sources of information to guide their design choices, such as a list of functions that an ideal collaborative writing tool should offer. This list has revealed several potential points for improvement.