ABSTRACT Current interactive user interface construction tools are often more of a hindrance than a benefit during the early stages of interface design. These tools take too much time to use and force designers to specify more of the design details than they wish at this stage. Most designers prefer to sketch early interface ideas on paper. I have developed an interactive tool called SILK that allows designers to quickly sketch an interface using an electronic pad and stylus. SILK preserves the important properties of pencil and paper: a rough drawing can be produced very quickly and the medium is very flexible. However, unlike a paper sketch, this electronic sketch is interactive. The designer can illustrate behaviors by sketching storyboards, which specify how the screen should change in response to end-user actions. In addition, it can be semi- automatically transformed into a complete, operational interface in a specified look-and-feel.