Information retrieval (IR) research and practice has traditionally been concerned with providing information seekers with a response to a request for information, and the evaluation of how good that response has been. As is recognized by this workshop, this \single-shot" approach to system support for information seeking, despite its successes, is inadequate in many ways as a model for support of information seeking in general. In particular, it ignores: that people interact with information objects during the course of information seeking episodes; that people have other goals during information seeking episodes than nding relevant documents; and, especially, that people do engage in information seeking episodes in what we might call search sessions. These conditions, which together have been understood to characterize what is called Interactive IR (IIR), require both new techniques for IIR support, and new methods and measures for evaluating such support. Both of these themselves require a much better understanding of why people engage in information seeking; their goals during information seeking; how they attempt to achieve their goals and the problems that they face in doing so; and how their activities during an information seeking session relate to and in uence the success of a search session. In this talk, I present a framework for addressing these issues, with special reference to the problems of evaluation of support for information seeking within, and over entire search sessions.