This text is intended to highlight the significance of uncertainty in the management of information, introduce methods of modelling uncertain information and discuss current and potential applications of such methods in information systems. It provides the reader with the following: a discussion of the kinds of information that are problematical; a discussion of the ways this impinges upon systems, eg. null values in relational databases; heuristics in rule-based decision-support systems; vagueness of keywords used in information retrieval; and appropriateness of cases selected in case-based decision-support. It also provides an exposition of means of modelling uncertain information including probability theory, possibility theory, fuzzy set theory and non-classical logics, and a review of the current and potential applications of handling uncertainty in information systems.