The growth of the Internet means everyone from system administrators to casual users are regularly confronted with making decisions on how to share data. Research suggests that even experts struggle to make these decisions accurately using current access-control mechanisms. As users start to share information across social and professional applications, usable access-control mechanisms that help prevent such semantic errors are all the more urgent. This project develops an interactive authoring paradigm that helps users identify and clarify policy inconsistencies before they turn into semantic errors. The envisioned tools examine policies and their consequences during authoring, alert users to potential inconsistencies (such as isolated documents shared more globally than most others), and ask questions in order to eliminate ambiguities. The challenge in building such proactive authoring tools lies in knowing what inconsistencies and issues to track without overwhelming a user with too much interaction. The proposal therefore combines user studies with tool building and evaluation. The intellectual merit of this project lies in its marriage of research on user behavior and logical tools to produce a new paradigm of policy authoring. Broader impacts come from building tools for mainstream end-users, guided by ethnographic studies of social-network users.