Hate speech can occur anywhere, as evidenced by the young men in khakis who shouted “Jews will not replace us” in Charlottesville, Virginia; the military’s use of Facebook to target the Muslim Rohingya in Myanmar; and a pastor’s call for ISIS to end the “homosexual curse” in South Africa in Capetown, South Africa. People use language to disparage others in person or online based on their race, national origin, religion, gender, gender identity, sexual orientation, age, handicap, or other identity-related characteristics. The MIT Press Essential Knowledge volume on hate speech covers what it is and is not its history and countermeasures.