Introducing iterative user interface design methods into the development processes of safety-critical software creates technical and methodological challenges. This article describes a new programming paradigm aimed at addressing some of these challenges: interaction-oriented programming. In this paradigm any piece of software consists of a hierarchical collection of components that can interact among themselves and with their environment, and its execution consists in propagating activation through interactions between components. We first describe the principles of interaction-oriented programming, and illustrate them by describing the basic components provided by the djnn programming framework to create interactive software. We then show how interactive programming provides a basis for formulating and checking properties that capture requirements on interactive components. The rest of the article is dedicated to example design and development scenarios that illustrate how development environments could leverage interactive programming in the future so as to jointly address the requirements of modern user interface design and safety-critical software development .