This chapter addresses the challenge of the configuration of modern interactive systems (ubiquitous, context-sensitive, mobile et al.) where it is difficult or impossible to predict the resources available for evolution, the criteria for judging the success of the evolution, and the degree to which human judgements must be involved in the evaluation process used to determine the configuration. A conceptual model of interactive system configuration over time is presented (known as interaction evolution) which relies upon the following steps; (i) identification of opportunities for change in a system, (ii) reflection on the available configuration alternatives, (iii) decision-making and (iv) implementation, and finally iteration of the process. This conceptual model underpins the development of a dynamic evolution environment based on a notion of configuration evaluation functions (here-after referred to as evaluation functions) that provides greater flexibility than current solutions and, when supported by appropriate tools, can provide a richer set of evaluation techniques and features that are difficult or impossible to implement in current systems. Specifically this approach has support for changes to the approach, style or mode of use for configuration. These features may result in more effective systems, less effort involved to configure them, and a greater degree of control for the user.