While the periodizing concept “post-truth” (PT) initially appeared in the United States as a key word of popular politics in the form “post-truth politics” or “post-truth society,” it quickly appeared in many languages. It is now the object of increasing scholarly attention and public debate. Its popular and academic treatments sometimes differ in respect to its meaning, but most associate it with communication forms such as fake or false news, rumors, hoaxes, and political lying. They also identify causes such as polarization and unethical politicians or unregulated social media; shoddy journalism; or simply the inevitable chaos ushered in by digital media technologies. PT is sometimes posited as a social and political condition whereby citizens or audiences and politicians no longer respect truth (e.g., climate science deniers or “birthers”) but simply accept as true what they believe or feel. However, more rigorously, PT is actually a breakdown of social trust, which encompasses what was formerly the major institutional truth-teller or publicist—the news media. What is accepted as popular truth is really a weak form of knowledge, opinion based on trust in those who supposedly know. Critical communication approaches locate its historical legacy in the earliest forms of political persuasion and questions of ethics and epistemology, such as those raised by Plato in the Gorgias. While there are timeless similarities, PT is a 21st-century phenomenon. It is not “after” truth but after a historical period where interlocking elite institutions were discoverers, producers, and gatekeepers of truth, accepted by social trust (the church, science, governments, the school, etc.). Critical scholars have identified a more complex historical set of factors, to which popular proposed solutions have been mostly blind. Modern origins of PT lie in the anxious elite negotiation of mass representative liberal democracy with proposals for organizing and deploying mass communication technologies. These elites consisted of pioneers in the influence or persuasion industries, closely associated with government and political practice and funding, and university research. These influence industries were increasingly accepted not just by business but also by (resource-rich) professional political actors. Their object was not policy education and argument to constituents but, increasingly strategically, emotion and attention management. PT can usefully be understood in the context of its historical emergence, through its popular forms and responses, such as rumors, conspiracies, hoaxes, fake news, fact-checking, and filter bubbles, as well as through its multiple effects—not the least of which the discourse of panic about it.