For many years basic visualisation, based around simple boxes and lines, has been done in an attempt to be able to ease some of the cognitive overload caused by program comprehension. The problems with such visualisations is that they can very easily become incomprehensible themselves by trying to force large amounts of information into a small space, relying solely on two dimensions for the representations and because generally the information is presented in a static way. There are many different issues that must be considered for three-dimensional visualisation, especially when those visualisations are of intangible software systems, and a selection of these are presented and discussed. - 1 - 1. Introduction Software visualisation is an important tool in the maintainer's armoury. It is a technique that can, when designed and used effectively, aid him in his quest to understand existing program code. This document provides an introduction to software visualisation issues, with pr...