Anti-Semitism is prejudice and discrimination against individuals or groups based on Jewish ethnicity, religion, or culture. This entry explores the modern history of the phenomenon, with a focus on the USA. The Holocaust was the most extreme extension of hatred of Jewish groups. However, there are many instances of anti-Semitism in Europe, the USA, and other regions of the world before and after Nazi Germany. Theories of anti-Semitism are discussed through sociological frameworks. More recently, the rise of anti-Semitism online and through social media has become prominent. This is linked to the history and sociology of this specific form of prejudice and discrimination.