Knowledge Systems is a term sometimes used to describe the institutional arrangements and interactions that seek to harness science, technology and other forms of expert knowledge for policy decision-making. In two inuential1 papers, Cash et al. (2002, 2003) suggested that eective knowledge systems for sustainable development can be created by managing the boundaries between knowledge and action through eective communication, translation and mediation. To achieve this boundary management, they propose a framework for assessing the eectiveness of evidence for use in decision-making using the criteria of credibility, salience and legitimacy. In this chapter I examine these concepts in some detail, in order to better understand the locus and character of the science-policy interface and how expertise and political authority interact at this boundary. I then examine Cash et al.’s formulation for what these interactions look like and to what extent their ideas can be helpful for climate adaptation scholars and practitioners. Since publication, their framework has been widely cited and continues to be used by those interested in the use of science for environmental policy.