Greta Thunberg. Alexandria Ocasio-Cortez. Anita Sarkeesian. Emma Gonzalez. When women are vocal about political and social issues, too-often they are flogged with attacks via social networking sites, comment sections, discussion boards, email, and direct message. Rather than targeting their ideas, the abuse targets their identities, pummeling them with rape threats, attacks on their appearance and presumed sexual behavior, and a cacophony of misogynistic, racist, xenophobic, and homophobic stereotypes and epithets. Like street harassment and sexual harassment in the workplace, digital harassment rejects women's implicit claims to be taken seriously as interlocutors, colleagues, and peers. Sarah Sobieraj shows that this online abuse is more than interpersonal bullying--it is a visceral response to the threat of equality in digital conversations and arenas that men would prefer to control. Thus identity-based attacks are particularly severe for those women who are seen as most out of line, such as those from racial, ethnic, and religious minority groups or who work in domains dominated by men, such as gaming, technology, politics, and sports. Feminists and women who don't conform to traditional gender norms are also frequently targeted. Drawing on interviews with over fifty women who have been on the receiving end of identity-based abuse online, Credible Threat explains why all of us should be concerned about the hostile climate women navigate online. This toxicity comes with economic, professional, and psychological costs for those targeted, but it also exacts societal-level costs that are rarely recognized: it erodes our civil liberties, diminishes our public discourse, thins the knowledge available to inform policy and electoral decision-making, and teaches all women that activism and public service are unappealing, high-risk endeavors to be avoided. Sobieraj traces these underexplored effects, showing that when identity-based attacks succeed in constraining women's use of digital publics, there are democratic consequences that cannot be ignored.