The article tackles the problem of defining and identifying experts. The conceptual analysis of what it means to be an expert relies on existing scholarship in social epistemology and sociology of expertise. It draws a portrait of experts as deeply immersed in specialist habits and practices, whose truth-tracing testimonies, publicity, and standards of inquiry bestow on them a tentative, context-dependent epistemic authority. This definition of expertise is closely connected with the question of their recognition by the lay public, i.e. how experts can (and should) signal their reliability and trustworthiness. The signalling is made possible through the culture of responsibility present in scientific practices along with the institutionalization of certain features of ‘epistemic vigilance’.