Object-oriented (OO) technology has been heralded as a solution to the problems of software engineering. The claims are that OO technology promotes understandability, extensibility, evolvabilty, reusability, and maintainability of systems and that OO systems are easy to understand and use. However, this technology has not been as successful as expected. An analysis of experiences and empirical studies reveals that the problem is not the technology per se but that the technology provides no support to software developers in performing the processes the technology requires. We present a cognitive model of software development that details the challenges software developers face in using OO technology. The model focuses on three aspects of software development—evolution, reuse and redesign, and domain orientation. We motivate this model with a variety of firsthand experiences and use it to assess current OO technology. Further, we present tools and evaluations that substantiate parts of this model. The model and tools indicate directions for future software development environment, looking beyond the technological possibilities of OO languages and beyond the context of individual developers and projects.