What are the defining qualities of ‘good advice’ in advanced democratic policy-making? In the UK, the employment of chief scientific advisers (CSAs) has served for several decades as a critical mechanism for incorporating ‘good scientific advice’ into policy decisions. Despite the ubiquity of this advisory model across major government departments however, the actual practices used by CSAs to provide advice to UK Government have barely been examined by social scientists. This paper documents the findings of a small study of CSAs, based upon sixteen semi-structured interviews and documentary analysis. Drawing on theoretical concepts from science and technology studies, it sets out tentative answers to two principal questions: 1) How do actors at the science-policy interface conceptualise the role and responsibilities of a CSA?; and 2) How do actors at the science-policy interface define ‘good advice’, and what kinds of practices do CSAs deploy to ensure that they meet this standard in going about their work? The paper’s findings have implications in particular for understandings of the role of boundary work in regulating both expert authority and policy-making credibility in the UK context (Gieryn, 1983; Bijker et al., 2009).