This article aims to provide a coherent and comprehensive theoretical framework of the main socio-epistemic features of social media. The first part consists of a concise discussion of the main epistemic consequences of personalised information filtering, with a focus on echo chambers and their many different implications. The middle section instead hosts an analytical investigation of the cognitive and epistemic environments of these platforms aimed at establishing whether, and to what extent, they allow their users to be epistemically vigilant with (...) respect to their sources and the content recommended to them. Finally, in the last part, of a more exquisitely normative nature, some strategies are proposed and discussed that, by reducing the epistemic opacity of social media, could contribute to greater epistemic justice within social media and, concurrently, to augmenting the epistemic autonomy of users. (shrink)