This article presents a case study in the use of problems in design. Problems- concrete examples of user goals whose accomplishment a system is intended to support-were used to describe the intended function of a graphical programming system and to manage the growth of the space of design alternatives for the system. Problems were also used to evaluate alternative designs: They served as bench marks for comparing both the solutions offered by differing designs and the work required of users to reach these solutions. The problem-centered design process includes a representation of design rationale in which the strengths and weaknesses of design alternatives in dealing with specific problems, rather than abstract connections among design issues, are central.