Antisemitism is defined as prejudice against or hatred of Jewish people and has existed for millennia. During the Holocaust, the Nazis and their collaborators murdered six million Jews across Europe. But antisemitism neither started nor ended there. What makes it one of the oldest and most persistent forms of hatred? Trace the history of the so-called "longest hatred" from ancient times to today and understand the intersection of four basic threads: religious, socio-economic, political, and racial. This background is crucial to understanding and combating antisemitism in our modern world.