Of all the aspects of computing, by far and away the most important for the vast majority of tasks, is the user interface. That is to say the way the user interacts with the computer to perform some task. Early computers had, what would now be described as a ``User Hostile'' interface; a user would have to learn obscure machine language and punch corresponding numerical codes onto paper tape to be fed into the machine (sometimes tearing as it did so!). In those days, computing was the province of a very few (a early estimate, of the number of electronic computers that the world would need, was placed at 6: 2 for the USA, 1 for Britain and 3 for everyone else!). We have come a long way since then and with the advent of a graphical interface, the computer is finally accessible to all. Indeed much of the interface design comes from studies on the way children learn and manipulate the world about them. A graphical interface consists of a number of elements, often drawn together into the acronym WIMP:-