A kohen (or cohen, Hebrew כּהן, "priest", pl. כּהנִים, kohanim or cohanim) has a separate status in Judaism. A kohen is a direct male descendant of the Biblical Aaron, brother of Moses. Another term for the descendants of Aaron are the Aaronites or Aaronids.
During the existence of the Temple in Jerusalem, kohanim performed specific duties vis-à-vis the daily and festival sacrificial offerings. The Kohen Gadol (High Priest) played a special role during the service of Yom Kippur. Today, kohanim retain a lesser though still somewhat distinct status within Judaism and remain bound by additional laws in Orthodox and, to a lesser extent, in Conservative Jewish communities. The Kohen, while having an exclusive role, is intended to be symbolic of all Jewish life: what Kohanim did inside the temple, other Jews should do outside in their daily lives. What Rabbi's and Torah Scholars do inside the Yeshiva, other Jews should do outside in their daily lives.
When the First and Second Temples were built, the kohanim assumed these same roles in these permanent structures, located on the Temple Mount in Jerusalem, Israel. They were divided into 24 work groups of seven to nine priests each. Those who served changed every Shabbat, but on the biblical festivals all 24 were present in the Temple.
Because Aaron was a member of the Tribe of Levi, all kohanim today are levites, by direct patrilineal descent. However, not all levites are kohanim. When the Temple existed, most services (i.e. the korbanot) could only be conducted by kohanim. Non-kohen levites (i.e. all those who descended from Levi, the son of Jacob, but not from Aaron) performed a variety of other Temple roles, most notably providing music and songs (Psalms) to accompany Temple ceremonies but also a variety of other duties including standing guard over the Temple and Temple Mount, construction, maintenance, and assisting the kohanim by washing their hands and feet before services. During the era of the Tabernacle, the non-kohen levites were employed in caring for and transporting the Tabernacle between travel destinations.
Certain imperfections could disqualify a kohen from serving in the Temple. Since the Temple was a place of beauty and the services that were held in it were designed to inspire visitors to thoughts of repentance and closeness to God, a less than physically perfect kohen would mar the atmosphere.
These blemishes include:
A Kohen who was afflicted with one of these imperfections was held unfit for service. However, should it be a correctable imperfection, the kohen would become eligible for service should the defect be corrected. At any time, he was permitted to eat of the holy food (same source as above, including adjacent verses and commentaries). Kohanim with these blemishes would be assigned to secondary roles in the Temple outside of performing the service itself.
The kohanim were rewarded for their role in the Temple through 24 special "priestly gifts." These were: 
Females were never allowed to serve in the Tabernacle or the Temple. They were permitted to consume or derive benefit from some of the 24 priestly gifts. If a kohen's daughter married a man from outside the kohanic line, she was no longer permitted to consume these priestly gifts. Conversely, the daughter of a non-priest who married a kohen took on the same rights as an unmarried daughter of a kohen.
The Talmud also orders the kohen to defile himself in the case of the death of a nasi (rabbinic leader of a religious academy). The Talmud relates that when Judah haNasi died, the priestly laws concerning defilement through contact with the dead were suspended for the day of his death.
Areas where Haredi and Modern Orthodox approaches might create different results include situations where a woman has been raped, kidnapped or held hostage, descendants of converts whose Judaism status turned out to be subject to doubt, ambiguous prior dating histories, and other potentially ambiguous or difficult situations.
Rape poses an especially poignant problem. The pain experienced by the families of Kohanim who were required to divorce their wives as the result of the rapes accompanying the capture of Jerusalem is alluded to in this Mishnah:
Orthodox Judaism maintains a belief in and hope for a restoration of a Third Temple in Jerusalem. Other denominations of Judaism, including the several in Orthodox Judaism, have different attitudes towards Kohanim, depending on their attitudes towards a Temple and Temple worship.
In Orthodox Judaism and to some extent in Conservative Judaism, Kohanim maintain their separate status in the following areas of modern life:
Every Monday, Thursday and Shabbat in Orthodox synagogues (and many Conservative ones as well), a portion from the Torah is read aloud in the original Hebrew in front of the congregation. On weekdays, this reading is divided into three; it is customary to call a Kohen for the first reading (aliyah), a Levite for the second reading, and a member of any other Tribe of Israel to the third reading. On Shabbat, the reading is divided into seven portions; a Kohen is called for the first aliyah and a Levite to the second, and a Yisroel for the rest.
If a kohen is not present, it is customary in many communities for a levite to take the first aliyah "bimkom Kohen" (in the place of a Kohen) and an Israelite the second and succeeding ones. This custom is not required by Halakha (Jewish religious law), however, and Israelites may be called up for all aliyot. In Orthodox Jewish circles, this custom has the status of law. The late 12th and early 13th century Rabbi Meir of Rothenberg ruled that in a community consisting entirely of Kohanim, the prohibition on calling Kohanim for anything but the first two and maftir aliyot creates a deadlock situation which should be resolved by calling women to the Torah for all the intermediate aliyot. Dr. Joel B. Wolowelsky, an author on the topic of the role of women in Judaism, has recently endorsed relying on this authority to permit the deliberate creation of minyanim composed entirely of Kohanim for the express purpose of giving women an opportunity to have an aliyah to the Torah in an Orthodox setting.
The Conservative Rabbinical Assembly's Committee on Jewish Law and Standards (CJLS), consistent with the Conservative movement's general view of the role of Kohanim, has ruled that the practice of calling a Kohen to the first aliyah represents a custom rather than a law, and that accordingly, a Conservative rabbi is not obligated to follow it. As such, in some Conservative synagogues, this practice is not followed.
Orthodox Judaism does not permit a bat kohen (daughter of a kohen) or bat levi (daughter of a levite) to participate in Nesiat Kapayim. The reason is that Nesiat Kapayim ("the raising of the hands") performed today is a direct continuation of the Temple ritual, and should be performed by those who were authentically eligible to do so in the Temple.
Regarding the ritual of the Priestly Blessing, the Conservative Movement's CJLS has also approved two positions. One view holds that a bat kohen may deliver the blessing; another view holds that a bat kohen is not permitted to participate in the Priestly Blessing because it is a continuation of a Temple ritual which women were not eligible to perform (Rabbis Stanley Bramnick and Judah Kagen, 1994; and a responsa by the Va'ad Halakha of the Masorti movement, Rabbi Reuven Hammer, 5748).
The majority of Reform Jews and Reconstructionist Jews consider all rules and ceremonies regarding the priesthood to be outdated. Many consider it to be anti-egalitarian, and thus discriminatory against Jews who are not Kohanim. Therefore the honors given to the Kohen during the Torah reading and in the performance of the Priestly Blessing are not observed in Reform or Reconstructionist Jewish communities. Many Reform and Reconstructionist Temples effectively forbid the practice of these laws and customs.
In Orthodox and Conservative circles, this ceremony is conducted as part of a festive meal. The Kohen first washes his hands and breaks bread, then calls for the father and the baby. The baby is typically brought in dressed in white and bedecked with gold jewelry, which the women in attendance contribute to beautify this mitzvah. The Kohen then engages the father in a formal dialogue, asking him whether he prefers to keep his money or his son. At the end of this exchange, the father hands over five silver coins (There is a debate about how much this should be in contemporary money. According to some calculations, this would be equal to approximately 101 grams of silver. It is a general custom to give a value more than what this would be worth, to enhance the mitzvah), and the kohen blesses him and his son. Though this ceremony should be conducted when the child is 29½ days (one lunar month) old, a first-born male who was never redeemed via Pidyon Haben may redeem himself later in life through a similar interaction with a kohen. Though no Kohen today can trace his lineage to a proven Kohen, a Yisroel technically has the right to demand the money be given back after the service.
The son of a Kohen or Levi and the son of the daughter of a Kohen or Levi need not be redeemed by the Pidyon HaBen rite. See Pidyon_HaBen (Exemptions)
Orthodox Judaism requires that the ritual be performed by male Kohanim. (Following the view of the Ramabam)
According to the Conservative Jewish view, there are some rabbinic sources that allow women to perform this ritual, and thus a bat kohen (daughter of a kohen) may perform the ceremony for a newborn son. However, it is forbidden to perform this ceremony on a first-born daughter.
Reform and Reconstructionist Jews generally do not perform this ceremony.
Modern-day kohanim are also prohibited from marrying a divorcee (even their own divorced wife), a woman who has committed adultery, been involved in incest, or had relations with a non-Jew. In compliance with Talmudic law, they also may not marry a female convert, out of concern for what may have occurred to her while she was a gentile. A born-Jewish woman who has had premarital relations may marry a kohen if and only if all of her partners were Jewish.
A child of a Jewish mother and non-Jewish father, while halakhically Jewish, is prohibited from marrying a kohen, by rabbinic law according to some opinions . The Sons of such a union do remain Kohanim. All modern orthodox synagogues will perform such a marriage.
In addition to the numerous restriction placed on Kohanim, Jews who are not Kohanim exemplify this designated role of the Kohen by granting him certain honorary roles within the community. Examples of such roles include the following....
The Kohen is given the option to recite blessings after the meal before the Yisroel if the Yisroel has lesser or equal knowledge of Jewish law compared to the Kohen.
It is a common misconception that the Kohen receives the finer portion of food at a meal or is called first to the Torah in order to give him honor. The Kohen is not entitled to the finer portion of a meal (Kitzur Shulchan Aruch), and is called first to the Torah in order to prevent arguments between Kohanim, Leviem and Yisroels. A Yisroel cannot be called to the Torah for the spot of a Kohen so long as one is present nor can a Kohen be called for the spot of a Yisroel so long as one is present.
Nearly all Rabbinic authorities maintain that in the next world (which is eternal), as opposed to this world where people are born inherently unequal, a person's status is determined by his effort alone. (Derech Hashem; Rabbi Moshe Chaim Luzzato)
So too, the honor due to a person who studies the Torah (Old Testament) and the Talmud (Jewish Oral Law) exceeds that due to a Kohen by far greater amounts. (Hilchot Deot; Rambam)
In addition, according to the vast majority of Rabbinic authorities, the honor given to a Kohen and Torah scholar is intended solely for the benefit of the person who is giving the honor; as opposed to the one who is receiving it.
"Better off a man be strangled by his placenta at birth than study Torah for the sake of honor" - Pirkei Avot (Ethics of our Fathers)
Regarding Kohanim it is said - "You think I am giving you authority? I am giving you servitude!" - Mesillat Yesharim (Path of the Just); Rabbi Moshe Chaim Luzzato) )
When Esau sold the birthright of the first born to Jacob, Rashi explains that the Priesthood was sold along with it, because by right the priesthood belongs to the first-born. Only when the first-born (along with the rest of Israel) sinned at the Golden calf, the priesthood was given to the Tribe of Levi, which had not been tainted by this incident.
Moses was supposed to receive the priesthood along with the leadership of the Jewish people, but when he argued with God that he should not be the leader, it was given to Aaron.
Aaron received the priesthood along with his children and any descendants that would be born subsequently. However, his grandson Pinchas (Phineas) had already been born, and did not receive the priesthood until he killed the prince of the tribe of Simon and the princess of the Midianites (). Thereafter, the priesthood has remained with the descendants of Aaron. However, when the Messiah comes, there is a tradition that it will revert back to the first born.
Orthodox Judaism retains the view that the privileges and status of Kohanim stem primarily from their offerings and activities in the Temple. Accordingly, in Orthodox Judaism only men can perform the Priestly Blessing and receive the first aliyah during the public Torah reading, and women are generally not permitted to officiate in a Pidyon HaBen ceremony. However, the question of what acts (if any) a Bat Kohen can perform in an Orthodox context is a subject of current discussion and debate in some Orthodox circles.
Some women's prayer groups which practice under the halakhic guidance of Modern Orthodox rabbis, and which conduct Torah readings for women only, have adapted a custom of calling a Bat Kohen for the first aliyah and a Bat Levi for the second.
Conservative Judaism, consistent with its view that sacrifices in the Temple will not be restored and in light of many congregations' commitment to gender (but not tribal) egalitarianism, interprets the Talmudic passages involved to permit elimination of most distinctions between male and female Kohanim in congregations that retain traditional tribal roles while modifying traditional gender roles. The Conservative movement bases this leniency on the view that the privileges of Kohen-hood come not from offering Temple offerings but solely from lineal sanctity, and that ceremonies like the Priestly Blessing should evolve from their Temple-based origins. (The argument for women's involvement in the Priestly Blessing acknowledges that only male Kohanim could perform this ritual in the days of the Temple, but that the ceremony is no longer rooted in Temple practice; its association with the Temple was by rabbinic decree; and rabbis therefore have the authority to permit the practice to evolve from its Temple-based roots). As a result, some Conservative synagogues permit a Bat Kohen to perform the Priestly Blessing and the Pidyon HaBen ceremony, and to receive the first aliyah during the Torah reading.
The law committee of the Masorti movement (the equivalent of Conservative Judaism) in Israel has ruled that women do not receive such aliyot and cannot perform such functions as a valid position (Rabbi Robert Harris, 5748). Therefore, not all Conservative congregations or rabbis permit these roles for Bnot Kohanim (daughters of priests). Moreover, many egalitarian-oriented Conservative synagogues have abolished traditional tribal roles and do not perform ceremonies involving Kohanim (such as the Priestly Blessing or calling a Kohen to the first aliyah), and many traditionalist-oriented Conservative synagogues have retained traditional gender roles and do not permit women to perform these roles at all.
Because Reform and Reconstructionist temples have abolished traditional tribal distinctions, roles, and identities on grounds of egalitarianism, a special status for a Bat Kohen has no significance in these movements.
There are numerous variations to the spelling of the surname Kohen. These are often corrupted by translation or transliteration into or from other languages, as exemplified below (not a complete list).
However, by no means are all Jews with these surnames kohanim. Additionally, some "kohen"-type surnames are considered stronger indications of the status than others. "Cohen" is one of the hardest to substantiate due to its sheer commonality.
In contemporary Israel, "Moshe Cohen" is the equivalent of "John Smith" in English-speaking countries - i.e., proverbially the most common of names.
The positioning of the kohen's hands during the Priestly Blessing was Leonard Nimoy's inspiration for Mr. Spock's Vulcan salute in the original Star Trek television series. Nimoy, raised an orthodox Jew (but not a kohen), used the salute when saying "live long and prosper."
Furthermore, the Star Trek Symbol is the same shape as the negative (air) space created between the Kohein's thumbs and forefingers, which some Kohanim touch while doing the Birchas Kohanim (Priestly Blessing). (There is some dispute as to whether or not to touch thumb to thumb and forefinger to forefinger while doing the blessing.
On the other hand, Robin Williams' characterization as extraterrestrial Mork (in the American sitcom Mork & Mindy) included a salutation with a position of his hands (along with the words: "Na-Nu, Na-Nu") which was very similar to kohen's hands.