The need for the developers of interactive systems to understand the eventual users and the work that the systems are to support is well known. How do developers obtain this understanding? They rely on intuition. They learn about users indirectly, by reading or being told about users’ needs. Sometimes they study or interact with users in constrained situations. Participatory design is a response to the recognition that these methods are often unsatisfactory—the utility and the usability of software could be markedly improved. Although good interactive systems exist, the difficulty of developing them is substantial. Many existing successes are the result of an undesirably long evolutionary process.