“Speak unto the children of Israel, that they bring thee a red heifer without spot, wherein no blemish is, and upon which never came yoke.” [Numbers 19:2]

The Red Heifer (Hebrew: פרה אדמה‎; Parah Adumah; translated to English as: Red Cow) in Judaism, is a sacrificial cow whose ashes are used for the ritual purification of people who come into contact with a corpse. The animal must not have hairs of any other color, it must be in perfect health, and it must never have been used to perform work. The heifer is then slain and burned outside of the camp Cedar wood, hyssop, and scarlet are added to the fire, and the remaining ashes are placed in a vessel containing pure water.

In order to purify a person who has become ritually contaminated by contact with a corpse, water from the vessel is sprinkled on him, using a bunch of hyssop, on the third and seventh day of the decontamination process (Numbers 19:18–19). The priest (kohen) who have performed the ritual then become impure themselves. The kohen who performs the ritual must then bathe himself and his clothes in water. He shall be deemed impure until evening.

The Mishnah, the central compilation of Rabbinic Oral Law, contains a tractate on the Red Heifer, tractate Parah in Seder Taharot, which explains the procedures involved. The tractate has no existing Gemara, although commentary on key elements of the procedure is found in the Gemarah for other tractates of the Talmud. According to Mishnah Parah, the presence of two black hairs invalidates a Red Heifer. In addition to the usual requirements of an unblemished animal for sacrifice, there are various other requirements, such as natural birth (Caesarian section renders a Heifer candidate invalid). The water must be "living" or spring water. This is a stronger requirement than for a mikvah. Rainwater accumulated in a cistern is permitted for a mikvah, but cannot be used in the Red Heifer ceremony. The Mishnah reports that in the days of the Temple in Jerusalem, water for the ritual came from the Spring of Shiloah. The ceremony involved was complex and detailed. To ensure complete ritual purity of those involved, enormous care was taken to ensure that no-one involved in the Red Heifer ceremony could have had any contact with the dead, and implements were made of materials, such as stone, which in Jewish law do not act as carriers for ritual impurities. The Mishnah recounts that children were used to draw and carry the water for the ceremony, children born and reared in isolation for the specific purpose of ensuring that they never came into contact with a corpse:

There were courtyards in Jerusalem built over [the virgin] rock and below them a hollow [was made] lest there might be a grave in the depths, and pregnant women were brought and bore their children there, and there they reared them. And oxen were brought, and on their backs were laid doors on top of which sat the children with cups of stone in their hands. When they arrived in Shiloah [the children] alighted, and filled [the cups with water], and mounted, and again sat on the doors. (Mishna Parah 3:2)

According to the Mishnah, the ceremony of the burning of the Red Heifer itself took place on the Mount of Olives. A pure priest slaughtered the Heifer, and totally sprinkled of its blood in the direction of the Temple seven times. The Red Heifer was then burnt on a pyre, together with crimson dyed wool, hyssop, and cedar wood.

The existence of a red heifer that conforms to all of the rigid requirements imposed by halakha is a biological anomaly. The animal must be entirely of one color, and there are a series of tests listed by the rabbis to ensure this, for instance, the hair of the cow must be absolutely straight (to ensure that the cow had not previously been yoked, as this is a disqualifier). According to Jewish tradition, only nine Red Heifers were actually slaughtered in the period extending from Moses to the destruction of the Second Temple. Mishnah Parah recounts eight, stating that Moses prepared the first, Ezra the second, Simon the Just and Yochanan the High Priest prepared two each, and Eliechonnai ben Hakkot and Hanameel the Egyptian prepared one each. (Mishna Parah 3:5)

The absolute rarity of the animal, combined with the mystical ritual in which it is used, have given the Red Heifer special status in Jewish tradition. It is cited as the prime example of a chok, or biblical law for which there is no apparent logic, and is therefore of absolute Divine origin. Because the state of ritual purity obtained through the ashes of a Red Heifer is a necessary prerequisite for participating in any Temple service, efforts have been made in modern times by Jews wanting to rebuild the Temple to locate a red heifer and recreate the ritual. However, multiple candidates have been disqualified, as late as 2002

In the Book of Daniel is a reference to a Red Heifer. In Daniel 12:10, HaShem tells Daniel that in the last days, "many shall be purified and made white"; a reference to the purification ritual of the Red Heifer, "Though your sins be as scarlet, they shall be as white as snow" (Isa 1:18, Num 19:6). The analogy appears to relate to a partner of the returning End Time messiah.

The Temple Institute, an organization dedicated to preparing the reconstruction of a Third Temple in Jerusalem, has been attempting to identify Red Heifer candidates consistent with the requirements of Numbers 19:1–22 and Mishnah Tractate Parah. In recent years, the Institute thought to have identified two candidates, one in 1997 and another in 2002. The Temple Institute had initially declared both kosher, but later found each to be unsuitable.

The non-canonical Epistle of Barnabas (8:1) explicitly equates the Red Heifer with Maran Yeshua. In the Besorah HaTovah (the Good News), the phrases "without the gate" (Hebrews 13:12) and "without the camp" (Numbers 19:3, Hebrews 13:13) have been taken to be not only an identification of Maran Yeshua with the Red Heifer, but an indication as to the location of the crucifixion (death).