Tohorot is the sixth order of the Mishnah

Mishnah

The Mishnah or Mishna is the first major written redaction of the Jewish oral traditions called the "Oral Torah". It is also the first major work of Rabbinic Judaism. It was redacted c...

 (also the Tosefta

Tosefta

The Tosefta is a compilation of the Jewish oral law from the period of the Mishnah.-Overview:...

 and Talmud

Talmud

The Talmud is a central text of mainstream Judaism. It takes the form of a record of rabbinic discussions pertaining to Jewish law, ethics, philosophy, customs and history....

). This order deals with the clean/unclean distinction and family purity. This is the longest of the orders in the Mishnah. There are 12 tractates:

1. Keilim
   Keilim
   Keilim is the first tractate in the Order of Tohorot in the Mishnah. It contains thirty chapters, making it the longest tractate in the entire Mishnah. The Tosefta on Keilim consists of twenty-five chapters, divided into Bava Kama , Bava Metzia , and Bava Batra of Keilim...
   
   : ("Vessels"); deals with a large array of various utensils and how they fare in terms of purity. 30 chapters, the longest in the Mishnah.
2. Oholot
   Oholot
   Oholot is the second tractate of the Order of Tohorot in the Mishnah. It consists of eighteen chapters, which discuss the ritual impurity of corpses, and the peculiar quality they have to make all objects in the same tent-like structure impure as well...
   
   : ("Tents"); deals with the uncleanness from a corpse and its peculiar property of "overshadowing" objects in the same tent-like structure as it.
3. Nega'im
   Nega'im
   Nega'im is the third tractate of the order of Tohorot in the Mishnah. It consists of fourteen chapters. Nega'im describes the various forms of tzaraath, a leprosy-like disease described in the Parshiyot of Tazria and Metzora in the Torah, which affected people, clothing, and homes...
   
   : ("Plagues"); deals with the laws of the tzaraath
   Tzaraath
   The Hebrew noun tzaraath describes a disfigurative condition mainly referred to in chapters 13-14 of Leviticus, as well as conditions equivalent to be "mildew" on clothes and houses.Tzaraath affects both animate...
   
   .
4. Parah: ("Cow"); deals largely with the laws of the Red Heifer.
5. Tohorot: ("Purities"); deals with miscellaneous laws of purity, especially the actual mechanics of contracting impurity and the laws of the impurity of food.
6. Mikva'ot
   Mikva'ot
   Tractate Mikva'ot is a section of the Mishna discussing the laws pertaining to the building and maintenance of a mikvah, a Jewish ritual bath...
   
   : ("Ritual Baths"); deals with the laws of the Mikvah
   Mikvah
   Mikveh is a bath used for the purpose of ritual immersion in Judaism...
   
   .
7. Niddah: ("Separation"); deals with the Niddah
   Niddah
   Niddah is a Hebrew term describing a woman during menstruation, or a woman who has menstruated and not yet completed the associated requirement of immersion in a mikveh ....
   
   , a woman either during her menstrual cycle
   Menstrual cycle
   The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....
   
    or shortly after having given birth.
8. Makhshirin: ("Preliminary acts of preparation"), the liquids that make food susceptible to tumah (ritual impurity)
9. Zavim: ("Seminal Emissions"); deals with the laws of a person who has ejaculated or has gonorrhea
   Gonorrhea
   Gonorrhea is a common sexually transmitted infection caused by the bacterium Neisseria gonorrhoeae. The usual symptoms in men are burning with urination and penile discharge. Women, on the other hand, are asymptomatic half the time or have vaginal discharge and pelvic pain...
   
   
10. Tevul Yom: ("Bathing (of the) day") deals with a special kind of impurity where the person immerses in a Mikvah
    Mikvah
    Mikveh is a bath used for the purpose of ritual immersion in Judaism...
    
     but is still unclean for the rest of the day.
11. Yadayim: ("Hands"); deals with a Rabbinic impurity related to the hands.
12. Uktzim
    Uktzim
    Uktzim is the last volume of the Order of Tohorot in the Mishnah. It is the last tractate in the Mishnah. It consists of three chapters...
    
    : ("Stalks"); deals with the impurity of the stalks of fruit.

Order of tractates

The traditional reasoning for the order of the tractates (according to Rambam) is as follows. Kelim is first as it introduces the levels of impurity, and dictates to which object the various impurities apply at all. Oholot follows because it outlines the most serious type of impurity. Negaim follows because it is next in severity and because, like a corpse, a metzorah transmits tent-inpurity. Parah follows as it outlines the purification for the severe impurities already dealt with. The next stage is lesser impurities (Tohorot) and their method of purification which is immersion (Mikvaot). Niddah follows as it is also a lesser impurity but it has the extra feature of applying to only a portion of people (i.e. to women). Makshirin, Zavim and Tevul Tom follow Niddah based on Scriptural order. The next stage down is impurities that are Rabbinic only (Yadaim). Finally, Uktzin is last as it is restricted and has no Scriptural source, the laws being derived from the reasoning of the Sages.

There is a Babylonian Gemara

Gemara

The Gemara is the component of the Talmud comprising rabbinical analysis of and commentary on the Mishnah. After the Mishnah was published by Rabbi Judah the Prince The Gemara (also transliterated Gemora or, less commonly, Gemorra; from Aramaic גמרא gamar; literally, "[to] study" or "learning by...

on only Niddah. This is because most of the other laws of purity do not apply when the Temple is not in existence. The Talmud Yerushalmi (Jerusalem Talmud) only covers four chapters of Niddah.