KOLUMBUS is one of many Web-based cooperative work systems that have been developed in the last few years. It was designed to support sharing structured documents with high granularity, i.e. documents split into paragraphs and images. Decomposing documents and making annotations provide contextual communication. Users don't work on entire documents or binary files (like MS Word docs), but rather on document parts, which can be navigated within KOLUMBUS' tree structure. Any comments or annotations are directly linked to the document parts to which they refer, providing a rich context representation. In this talk, basic concepts and functionalities of KOLUMBUS will be presented, as well as some of the social and technical problems we encountered. Development issues will be addressed, particularly regarding a projected redesign of KOLUMBUS.