Interactive computer networks create new opportunities for the co-operative structuring of information which would be impossible to implement within a paper-based medium. Methods are described for co-operatively indexing, evaluating and synthesizing infor-mati3n through well-specified interactions by many users with a common database. These methods are based on the use of a structured representation for reasoning and debate, in which conclusions are explicitly justified or negated by individual items of evidence. Through debates on the accuracy of information and on aspects of the structures themselves, a large number of users can co-operatively rank all available items of information in terms of significance and relevance to each topic. Individual users can then choose the depth to which they wish to examine these structures for the purposes at hand. The function of this debate is not to arrive at specific conclusions, but rather to collect and order the best available evidence on each topic. By representing the basic structure of each field of knowledge, the system would function at one level as an information retrieval system in which documents are indexed, evaluated and ranked in the context of each topic of inquiry. At a deeper level, the system would encode knowledge in the argument structures themselves. This use of an interactive system for structuring information offers further opportunities for improving the accuracy, integration and accessibility of information.