Nidda

Nidda or Niddah could refer to:


 * Niddah, a concept in Judaism, name for any woman during menstruation, or a woman who has menstruated and not yet completed the associated requirement of immersion in a mikveh (ritual bath)
 * Niddah (Talmud), a tractate in the Mishna and Talmud, on the Halakha of Niddah in the order of Mishnah Tohorot.
 * Nidda, Hesse, a town in Germany
 * County of Nidda, medieval polity in Germany
 * Nidda (river), a river in Germany
 * County of Nidda, a state of the Holy Roman Empire from 1104-1450