Using examples of implemented layout decisions, and from performance-based research on the effects that layout has on readers this paper proposes seven reasons why the layout of documents is important. These reasons range from economic to psychological. The importance of specific layout features will often differ for those generating documents from an information resource and for those seeking to capture existing documents. Many layout problems arise when documents are transferred across media (e.g. print to computer monitor to Personal Digital Assistant). The present discussion emphasises the value of maintaining a functional equivalence of layout features (e.g. visual grouping) rather than preserving formal identity (e.g. spacing). A prerequisite for doing this is an understanding of how layout features influence reading activities. It is suggested that although there are gaps in our knowledge of readers’ search and decisionmaking processes it would nevertheless be possible to devise a simulated reader that responded to layout features, such as the relation between text and graphics, in the way that most readers will. This would be a useful tool for maintaining functional equivalence when documents are moved across media.