Incels. Anti Vaxxers. Conspiracy theorists. Neo-Nazis. Once, these groups all belonged on the fringes of the political spectrum. Today, accelerated by a pandemic, global conflict and rapid technological change, their ideas are becoming more widespread: QAnon proponents run for U.S. Congress, neo-fascists win elections in Europe, and celebrity influencers like Kanye West spread dangerous myths to millions. Going Mainstream asks the question: What is happening here? Going undercover online and in person, UK counter-extremism expert Julia Ebner reveals how, united by a shared sense of grievance and scepticism about institutions, radicalised individuals are influencing the mainstream as never before. Hidden from public scrutiny, they leverage social media to create alternative information ecosystems and build sophisticated networks funded by dark money. Ebner's candid conversations with extremists offer a nuanced and gripping insight into why people have turned to the fringes. She explores why outlandish ideas have taken hold and disinformation is spreading faster than ever. And she speaks to the activists and educators who are fighting to turn the tide.