Antisemitism (also spelled anti-semitism or anti-Semitism) is hostility to, prejudice towards, or discrimination against Jews. A person who holds such positions is called an antisemite. Antisemitism is considered to be a form of racism.

Antisemitism has historically been manifested in many ways, ranging from expressions of hatred of or discrimination against individual Jews to organized pogroms by mobs, police forces, or genocide. Although the term did not come into common usage until the 19th century, it is also applied to previous and later anti-Jewish incidents. Notable instances of persecution include the Rhineland massacres preceding the First Crusade in 1096, the Edict of Expulsion from England in 1290, the 1348–1351 persecution of Jews during the Black Death, the massacres of Spanish Jews in 1391, the persecutions of the Spanish Inquisition, the expulsion from Spain in 1492, the Cossack massacres in Ukraine from 1648 to 1657, various anti-Jewish pogroms in the Russian Empire between 1821 and 1906, the 1894–1906 Dreyfus affair in France, the Holocaust in German-occupied Europe during World War II and Soviet anti-Jewish policies. Though historically most manifestations of antisemitism have taken place in Christian Europe, since the early 20th century antisemitism has increased in the Middle East.

The root word Semite gives the false impression that antisemitism is directed against all Semitic people, e.g., including Arabs, Assyrians, and Arameans. The compound word Antisemitismus ('antisemitism') was first used in print in Germany in 1879 as a scientific-sounding term for Judenhass ('Jew-hatred'), and this has been its common use since then.