The introduction to this collection maps the rise of true crime as a multimedia, participatory genre with an active and diverse fandom. It documents the true crime genre’s pressing ethical issues such as the marginalisation of victims, the centreing of criminals, and the generation of fear and paranoia in its audiences. As true crime audiences’ perceptions have been shaped by such issues, the growth of participatory culture has also enabled unprecedented opportunities for audiences to emotionally invest in and engage with true crime, often via user-generated productions that circulate on social media platforms. This introduction observes that the proliferation of voices enabled by true crime’s intersection with participatory culture could be changing the genre’s ethical landscape as audiences very publicly reflect upon, argue about and bond over the genre’s problematic conventions. Finally, the introduction delineates the collection’s three sections: Part One, “The Ethics of Watching and Doing,” which concerns the ethical pitfalls of true crime content on social media; Part Two, “Participatory Culture,” which deals with the acts of participatory culture that define not only contemporary true crime fandom but also nearly all digitally-based fan activities; and Part Three, “True Crime Communities,” which considers the enthusiasts who both consume true crime and actively seek out others online to share their interests.