This is a book about how information systems can be made to manage information permeated with uncertainty. This subject is at the intersection of two areas of knowledge: information systems is an area that concentrates on the design of practical systems that can store and retrieve information; uncertainty modelling is an area in artificial intelligence concerned with accurate representation of uncertain information and with inference and decision-making under conditions infused with uncertainty. The first part of the text describes issues and challenges in the area of imperfect information that confront information systems, and the second part covers the principal theories for modelling imperfect information, and shows how these theories may be adapted to information systems. All chapters present solutions that have been applied, and the experiences that have been gained from those solutions. The material has been closely edited by the book's editors for content, consistency and style.