Jewish ritual immersion has been practiced among Jews for over two thousand years, from the late second century BCE until today. Although much has been written in recent years on various aspects of this ritual as it was performed in different periods, no study has surveyed the practice from the perspective of the longue durée—from its earliest manifestations until the modern era. The present study does just that; it examines the textual evidence and material remains that shed light on how the ritual was performed over the course of the past two millennia, exploring who practiced it in each period, and how it developed and changed over the centuries.