Part I: Computational Models and Systems. About the Authors. Preface: Intelligent Help Systems for UNIX. Editorial Part I: Intelligent Help Systems for UNIX; Computational Models and Systems. An Intelligent Human-Computer Interface for Provision of On-Line Help; J. Jerrams-Smith. Virtues and Problems of an Active Help System for UNIX; M. Virvou, et al. The Berkeley UNIX Consultant Project; R. Wilensky, et al. The OSCON Operating System Consultant; P. Mc Kevitt. USCSH: An Active Intelligent Assistance System; M. Matthews, et al. Part II: Planning and Knowledge Representation. Editorial Part II: Intelligent Help Systems for UNIX: Planning and Knowledge Representation. The SINIX Consultant - Towards a Theoretical Treatment of Plan Recognition; M. Hecking. Plan Realization for Complex Command Interaction in the UNIX Help Domain; S.J. Hegner. An Assumption-based Truth Maintenance System in Active Aid for UNIX Users; J. Jones, et al. What Do You Know about Mail? Knowledge Representation in the SINIX Consultant; C. Kemke. Part III: Natural Language Dialogue. Editorial Part III: Intelligent Help Systems for UNIX: Natural Language Dialogue. Planning Intelligent Responses in a Natural Language System; D.N. Chin. Strategies for Expressing Concise, Helpful Answers; D.N. Chin. Evaluating Plan Recognition Systems: Three Properties of a Good Explanation; J. Mayfield. Representing UNIX Domain Metaphors; J.H. Martin. Using Justification Patterns to Advise Novice UNIX Users; A. Quilici.