FOA (Formatting Object Authoring) is an authoring tool that applies rich styling to XML content. It allows the styling to be re-used across multiple documents. It also allows the author to build or import a library of style components. It is based on XSL-FO, the W3C- defined markup language, whose aim is to add rich styling to XML content, especially for paginated documents. The architecture of FOA permits the author to create and modify style sets, and also allows these styles to be re-applied to different XML content. The tool generates an XSL stylesheet, based on the style information, that takes the XML content and produces an XSL-FO document, which can then be rendered into different output formats. An extension to an XSL-FO renderer allows the author to preview the output within the authoring tool. The architecture was developed as my part of the co-supervision of a Master Thesis, in collaboration with the University of Genoa, during which significant pieces of FOA have also been implemented. 11 Pages