An expert is commonly considered to be somebody who possesses the right kind of knowledge and skills to find out true answers for questions in a domain. However, this common conception that focuses only on an individual’s knowledge and skills is not very useful to understand the epistemically interdependent nature of contemporary scientific expertise, which becomes increasingly more relevant due to the rise of large interdisciplinary research collaborations. The typical scientific expert today relies substantially on complex scientific instruments and numerous (...) other experts in forming expert judgment. Moreover, we have research collaborations where multiple scientists interact in a way that gives rise to distributed cognitive systems, which can act as a single informant. Accordingly, our concept of scientific expertise should not consist only in individual knowledge and skills, but also accommodate epistemic dependence and collective knowledge production. To this aim, this paper proposes a reconstruction of the concept of scientific expertise as informant reliability by building on the virtue-epistemological account of epistemic competences and theories of extended and distributed cognition. Considered in reference to the social epistemic function of expertise, a scientific expert should be conceived as a reliable informant in a scientific domain, which implies that when consulted on matters in that domain they assert competently, honestly, and completely. Competent expert assertion involves the epistemic responsibility to draw on nothing but the highest degree of epistemic competence relevant to the given context. Thus, being a reliable informant may require one to draw on an extended epistemic competence that goes beyond one’s individual competence, or to form supra-individual or group-informants that manifest collectively the kind of complex epistemic competence required for the investigation of certain research questions. (shrink)