The general aim of the work reported in this thesis is to investigate the viability of applying theories and principles from the field of natural language pragmatics to that of human-computer interaction. In pursuing this aim, the research falls broadly into three phases. The first of these is the exploitation and adaptation of the Gricean Cooperative Principle, its maxims and inferential rules to situations of computer use which do not employ natural language as the medium of communication. The purpose of this endeavour is to provide a novel and revealing analysis of non natural language interaction and to establish principles for dialogue design, the application of which enhance the quality of communication between system and user in such situations. The second phase concerns the application of the adapted Gricean principles to the design of a dialogue management system, intended to address some of the problems which other research has revealed users to experience in using the standard UNIX® shell interface. This second phase resulted in the production of the QDOS system, which is both a simulation of part of the UNIX® file system and an implementation of the proposed dialogue management system. This software acts as the vehicle for all subsequent evaluative exercises constituting the third phase. This takes the form of an evaluation of the QDOS system and its theoretical underpinning, based on a two-condition experiment and a protocol analysis, involving a number of experimental subjects. This research provides an original application of the Gricean Cooperative Principle in human-computer interaction and a theoretical and practical demonstration of the validity of this endeavour. It also adduces an analysis of the UNIX® interface and its vagaries in terms of a principled and consistent set of criteria as well as identifying a significant class of dialogue breakdown, the circumstances and incidence of which cut across issues of interface style.