Ecological approaches to psychology suggest succinct accounts ofeasily-used artifacts. Affordances are properties of the world that are compatible with and relevant for people's interactions. When affordances are perceptible, they offer a direct link between perception and action; hidden and false affordances lead to mistakes. Complex actions can be understood in terms of groups of affordances that are sequential in time or nested in space, and in terms of the abilities of different media to reveal them. I illustrate this discussion with several examples of interface techniques, and suggest that the concept of affordances can provide a useful tool for user-centered analyses of technologies.