Why efforts to moderate harmful content on social media fail to stop extremistsContent moderation on social media has become one of the most daunting challenges of our time. Nowhere is the need for action more urgent than in the fight against terrorism and extremism. Yet despite mass content takedowns, account suspensions, and mounting pressure on technology companies to do more, hate thrives online. Safe Havens for Hate looks at how content moderation shapes the tactics of harmful content producers on a wide range of social media platforms. Drawing on a wealth of original data on more than a hundred militant and hate organizations around the world, Tamar Mitts shows how differing moderation standards across platforms create safe havens that allow these actors to organize, launch campaigns, and mobilize supporters. She reveals how the structure of the information environment shapes the cross-platform activity of extremist organizations and movements such as the Islamic State, the Proud Boys, the Oath Keepers, and QAnon, and highlights the need to consider the online ecosystem, not just individual platforms, when developing strategies to combat extremism. Taking readers to the frontlines of the digital battleground where dangerous organizations operate, Safe Havens for Hate sheds critical light on how governments and technology companies grapple with the tension between censorship and free speech when faced with violence, hate, and extremism.