Human-computer interaction (HCI) study is the region of intersection between psychology and the social sciences, on the one hand, and computer science and technology, on the other. Human-computer interaction has progressively integrated its scientific concerns with the engineering goal of improving the usability of computer systems and applications, which has resulted in a body of technical knowledge and methodology. HCI continues to provide a challenging test domain for apply for and developing psychological and social theory in the context of technology development and use.

Human-computer interaction is a science of design. It seeks to understand and support human beings interacting with and through technology. Much of the structure of this interaction derives from the technology, and many of the interventions must be made through the design of technology. HCI is not merely applied psychology. It has guided and developed the basic science as much as it has taken direction from it. It illustrates possibilities as a design science.

The leading idea is that designers often need to do design to adequately understand design problems. One empirical case analysis of the development of the IBM 360 Operating System, one of the largest planned software design projects. The project manager concluded that system and software designers should plan to discard at least one of their final programs. This was a striking lesson to draw and carried with it many implications. For example, formal and comprehensive planning and specification aid will have limited utility in supporting such and iterative design process.

Iterative development shifted the focus of usability evaluation from summative to formative. Formal experiments are fine for determining which of two designs are better on a set of dimensions, but they are neither flexible nor rich enough to guide continual redesign. "Thinking aloud" became the central empirical, formative evaluation method in HCI (Wright & Converse 1992).

The role of prior knowledge in learning to use computer systems was another focus of user modeling work. It was widely noted that new users tried to understand computers as analogical extensions of familiar activities and objects (Douglas & Moran 1983). This observation led to a variety of user interface metaphors, such as the now pervasive desktop interface, and a methods for user interface control and display called "direct manipulation". This also led to theories of user interface (Carroll 1989). This work began the concept of the "active user," hypothesizing and trying to make sense of a very complex environment. It led to emphases on designing for learning by doing and from error.

Iterative development is consistent with the real nature of design. It emphasizes the discovery of new goals, the role of prototyping and evaluation, and the importance of involving diverse users. Usability engineering became the banner under which diverse methodology were carried out. There were three key notions. First, it was proposed that iterative development be managed according to explicit and measurable objectives. The second key notion was a call to broaden the empirical scope of design. A variety of approaches and techniques for user participation were developed, many of which emphasized low tech, cooperative activities to facilitate collaboration between users, who bring expertise on the work situation, and developers, who bring expertise on technology. The third key notion in usability engineering was cost effectiveness. It is expensive to carry out many cycles of prototyping, evaluation, and redesign. Developers need to employ efficient methods throughout and to know when they have reached diminishing returns.

This approach went beyond prior formulations of user involvement by describing broader and more active roles for users. In participatory design, users are involved in setting design goals and planning prototypes, instead of becoming involved only after initial prototypes exist. Field study approaches are not equivalent to user participation. Often field studies bring to light facts in the background of the context of use, circumstances of which the users themselves are unaware. Conversely, field studies cannot reveal the perspectives and insights users bring to the development process as designers.

The emergence of HCI in the past has illustrates the possibilityof psychological inquiry in the context of system development and of progress with fundamental issues joined with engineering design. It demonstrates how the complex problem solving of system development is not a straightforward scaling of laboratory-based studies of puzzles. Laboratory situations are models of real situations in which people are deprived of social and tool resources that constitutes those situations. Human behavior and experience both adapt to and transform social and technological context. Human activities motivate the creation of new tools, but these in turn alter activities, which in time motivates further tools. The context of behavior and experience is changing more rapidly, and perhaps more profound than ever before in history.