The Tractate Niddah is the only tractate in the Order of Taharot that contains both Mishnah and Talmud. As its name indicates, the major focus of this tractate is to clarify the laws of the niddah (a woman in menstruation.) These laws are the basis for taharat mishpacha (family purity) and the regular use of the mikveh in Jewish married life.

The Talmud concludes the tractate with an Aggadic teaching about the importance of studying halachah (Jewish law) everyday:

The school of Elijah teaches: Whoever repeats halachahs [ie: one who studies Jewish law] every day may rest assured that he will be a denizen of the World to Come, for it is said, "Halichot — the world is his." Read not halichot (goings) but halachot (laws).