Sustainability is a contested, normative concept that frames decisions using a holistic, longterm perspective based on environmental, social, and economic considerations. Cities have taken the lead in incorporating this framework into decision-making processes, from Local Agenda 21 processes to city- specific planning. However, as cities have begun to integrate sustainability into decision-making, they have been confronted with several concerns regarding the use of information and indicators. The contested nature of sustainability makes the collection and use of information inherently political and occasionally problematic. Indicators can serve multiple purposes in the policy process, from system monitoring to issue framing and coalition building. As problems or actors’ understanding of them changes, new indicators may be required and old information used in new ways. However, the way indicators are used by different actors in the policy-making process is not well understood. This paper will seek to answer this question by studying the evolving sustainability information system in Seattle, as well as the role of individual indicator users within the city. Seattle, which has used sustainability indicators for over two decades, is an international leader in this area. I use a case study approach that evaluates historical materials, government and organizational documents, and interviews with decision-makers. I highlight the various ways that actors in Seattle collect and use information related to sustainability in policy-making. I demonstrate that, although actors at different scales inside and outside government use information in multiple ways to influence policy, different types of actors emphasize specific uses based on their capacity, goals, and the needs of the system. This creates an evolving sustainability system in which actors work together to provide and discuss information, frame sustainability, and create effective policy to improve sustainability in the city.