Nature conservation policy relies on ecological science for strategies and priorities. Science-based instruments such as ecological indicators are used to assess the quality of conservation areas. It is assumed that these instruments objectify nature quality, provide nature conservation policy with a scientific basis, and enhance decision-making processes. But can nature quality be objectified? Can ecological indicators be scientific and policy relevant at the same time? These and other questions are addressed in this study that focuses on the roles of science, expertise, and ecological indicators in Dutch nature conservation policy for the Wadden Sea and the Veluwe.