Story understanding programs are often designed to answer questions to demonstrate that they have adequately understood a story (e.g., [Leh78]). In contrast, we claim that asking questions is central to understanding. Reading a story involves the generation of questions, which in turn focus the understander on the relevant aspects of the story as it reads further. We are interested in the kinds of questions that people ask as they read. In this paper, we talk about the origin of these questions in the basic cycle of understanding, and their effect on processing. We present an understanding algorithm based on our theory of questions, which we have implemented in a computer program called AQUA (Asking Questions and Understanding Answers).