A description of the principles of and practices in human-computer interfacing, based on applied psychology, while integrating the approach with methods of software engineering. Tasks analysis, command language grammar, display and control interfaces and interface evaluation are examined. The study aims to bridge the gap between psychology, ergonomics and computer science and to give software developers a greater awareness of the human user for whom they are ultimately designing - as well as guidelines for good human features in an interface design and a design framework within which to work.