This article offers a distinctive way of grounding the regulative duties held by social media companies (SMCs). One function of the democratic state is to provide what we term the right to democratic epistemic participation within the public sphere. But social media has transformed our public sphere, such that SMCs now facilitate citizens’ right to democratic epistemic participation and do so on a scale that was previously impossible. We argue that this role of SMCs in expanding the scope of what counts as fair democratic epistemic participation, and in becoming the providers of access to the digital public sphere, brings with it duties of regulation.