Design rules, in the form of standards and guidelines, provide designers with directions for a good and quality design with the intention of increasing the usability of a system.

Software companies produce sets of guidelines for their own developers to follow. These collections are called house standards, sometimes referred to as house style guides. These are more important in industry, especially in large organisations where commonality can be vital. There are two main types of style guides: commercial style guides and corporate style guides.

Hardware and software manufacturers produce commercial style guides and corporate style guides are developed by companies for their own internal use. The advantage of using these guides is to enhance usability of a product through consistency. However, there are other reasons, for example, software developed for Microsoft, Apple Macintosh or IBM PC maintains its "look and feel;" across many product lines.

Though commercial guides often contain high level design principles, in most cases these documents are based on low level design rules which have been developed from high level design principles. If an organisation aims to develop their own corporate style guides for software, generally the starting point will be one of the commercial style guides.

Many design style questions have to be addressed more specifically when developing corporate style guides. For example, how should dialog windows to be organised? Which styles - colour and fonts etc, should be used ?

The roots for design rules may be psychological, cognitive, ergonomic, sociological or computational, but may, or may not be, supported by empirical evidence.