The twenty-first century is no stranger to genocides, war crimes, and crimes against humanity. What is distinctive about this century, however, is the role of new technologies—cyber-operations, digital platforms, and AI—in enabling such atrocities. Perpetrators are increasingly online: they are leveraging algorithmic systems to organize, fund, propagandize, celebrate, deny, and execute violence in harrowingly innovative ways. Unlike in centuries prior, atrocity perpetrators now possess a distinct Achilles' heel: the very technologies they rely on to commit their crimes. Curiously, very little attention has been afforded to how offensive cyber-operations and online (AI-generated) influence campaigns might help prevent such atrocities in the digital age. Algorithms & Atrocities mounts the first sustained account and defense of "cyber humanitarian interventions" (CHIs)—sophisticated cyber-operations and targeted influence campaigns that aim to disrupt perpetrators' means and motivations for carnage. By disrupting "means", CHIs involve targeting the perpetrators' digital infrastructure—breaching, disabling, damaging, or otherwise intercepting the systems used to coordinate and carry out atrocity crimes. By disrupting perpetrators' "motivations", CHIs aim to influence the perpetrators themselves via "targeted information campaigns"—tailor-made (AI-generated) online content that undermines perpetrators' desire to kill. If such corrective epistemic interventions fail, then this book asks: might there be a case for spreading "atrocity suppressing disinformation campaigns" as corrosive epistemic interventions? This book navigates the ethically fraught issues attendant with CHIs and identifies which moral agents bear duties to operationalize such interventions. The more digitally dependent perpetrators of atrocities become, the more vulnerable they will be to being hacked for humanitarian ends. Algorithms & Atrocities is a first step toward bridging the gap between research on new technologies, atrocity prevention, and ethics.