PREFACE After 15 year of pursing rough set theory and its application we can say that it has reach a certain degree of maturity. In recent years we witnessed a rapid grow of interest in rough set theory and its application, world wide. Many international workshops, conferences and seminars included rough sets in their programs. A large number of high quality papers have been published recently on various aspects of rough sets and wide range of applications. In particular algebraic and topological foundations of rough sets attracted attention of many researchers. Various logics based on the rough set concept are blossoming in recent years. Connection of rough sets and probabilistic reasoning methods have deserved also due attention of many researchers. Several extension of the ``basic'' model of rough set have been proposed and investigated. A variety of new methods of rule generation based on the rough set approach have been developed. The connection of rough set theory and many other theories, in particular dealing with vagueness and uncertainty, has been clarified. In particular relation to fuzzy set theory, the theory of evidence, boolean reasoning methods, discriminate analysis and decision theory has been extensively investigated. Various real life-application of rough sets have shown its usefulness in many domains. Medicine, pharmacology, banking, market research, engineering, speech recognition, material sciences, control, linguistic, databases are just some exemplary fields of application, where rough set theory has demonstrated its usefulness. Very promising new areas of application of the rough set concept seems to emerge in the near future. They include rough control, rough data bases, rough information retrieval and rough neural network and others. No doubt that rough set theory can contribute essentially to machine learning and data mining. Despite of many achievements a wide variety of problems still requires consideration and extensive research. Particularly important seems to be hardware implementation of rough computer. Such computer is badly needed to pursue many applications. This Bulletin can contribute essentially to exchange information about current research in rough sets and provide guidelines for future directions. I am deeply convinced that the Bulletins will play an important role in pursuing further rough set development and applications. Zdzislaw Pawlak