The blueprint for a house (its architectural design) is not complete without a representation of doors, windows, and utility connections for water, electricity, and telephone (not to mention cable TV). The "doors", windows, and utility connections" for computer software make up the interface design of a system.

Interface design focuses on three areas of concern: (1) the design of interfaces between software components, (2) the design of interfaces between the software and other nonhuman producers and consumers of information (i.e., other external entities), and (3) the design of the interface between a human (i.e., the user) and the computer. In this chapter we focus exclusively on the third interface design category—user interface design.