Auditory overviews have the potential to improve the quality of auditory interfaces. However, in order to apply overviews well, we must understand them. Specifically, what are they and what is their impact? This thesis presents six characteristics that overviews should have. They should be a structured representation of the detailed information, define the scope of the material, guide the user, show context and patterns in the data, encourage exploration of the detail and represent the current state of the data. These characteristics are guided by a systematic review of visual overview research, analysis of established visual overviews and evaluation of how these characteristics fit current auditory overviews. The second half of the thesis evaluates how the addition of an overview impacts user interaction. While the overviews do not improve performance, they do change the navigation patterns from one of data exploration and discovery to guided and directed information seeking. With these two contributions, we gain a better understanding of how overviews work in an auditory interface and how they might be exploited more effectively.