The papers in this volume are extended versions of presentations at the fourth International Conference on Information Processing and Management of Uncertainty in Knowledge-based Systems (IPMU), held in Palma de Mallorca, July 6-10, 1992. The conference focused on issues related to the acquisition, representation, management, and transmission of information in knowledge-based and decision-making systems. The book is focused on methodologies related to artificial intelligence, including both theoretical and applied papers. The first section of the book is devoted to non-monotonic reasoning and the managementof default knowledge. The second section deals with methods using non-classical logics to deal with imperfect knowledge and to represent its spatial and temporal components. The third section presents various methods for the acquisition of uncertain and imprecise knowledge. The fourthsection is concerned with the use of qualitative, uncertain, temporal, and ambiguous pieces of information in knowledge-based systems, expert systems, and process controllers. The last section contains papers using artificial neural network methodologies.