This volume contains papers from the International Workshop on Rough Sets and knowledge Discovery, held in Banff, Alberta, Canada, from the 12 - 15 October 1993. It includes application reports and theory oriented papers by leading professionals in both. of these important areas of research. There are comprehensive sections on the following topics: knowledge discovery methodologies and applications; fundamental research in the theory of rough sets and its extensions; machine learning applications of the rough sets approach (including presentation of some new learning methods); reasoning from uncertain information using a combination of fuzzy and rough sets methods; and applications of the methodologies , areas such as market analysis, medical diagnosis, and image processing. The resulting volume will be of interest to researchers and developers of systems for knowledge acquisition, decision support and machine discovery.