In this article, we propose the concept of meta-User Interface (meta-UI) as the set of functions (along with their user interfaces) that are necessary and sufficient to control and evaluate the state of interactive ambient spaces. This set is meta-, since it serves as an umbrella beyond the domain-dependent services that support human activities in an ambient interactive space. They are User Interface-oriented since their role is to help the user to control and evaluate the state of this space. We present a dimension space to classify, compare, and contrast disparate research efforts in the area of meta-UI’s. We then exploit the generative power of our design space to suggest directions for future research.