This book is dedicated to the memory of Zdzislaw Pawlak, a great scientist and a great human being. A short perspective on the life and work of Zdzislaw Pawlak is given at the beginning of this volume. During his lifetime, the research interests of Pawlak were rich and varied. His research ranged from his pioneering work on knowledge description systems and rough sets during the 1970s and 1980s to his work on the design of computers, information retrieval, modeling conflict analysis and negotiation, genetic grammars and molecular computing. One should also mention his active lifelong interest in painting, photography and poetry. During his lifetime, Pawlak nurtured worldwide interest in approximation, approximate reasoning and rough set theory and its applications. A compelling evidence of the scientific influence of Pawlak is the literature on rough sets that now includes over 4000 publications as well as the growth and maturity of the International Rough Set Society. Many papers that appear in this book reflect the profound influence of a number of research initiatives by Pawlak in a whole range of research areas. It can also be inferred from the papers included in this volume, that research concerning the foundations and applications of rough sets remains a vivid and still growing research area worldwide. During the past 35 years since the introduction of knowledge description systems in the 1970s by Pawlak, the theory and applications of rough sets as well as the advent of approximation spaces to facilitate perception and observation concerning classes of objects has developed in a truly impressive way.