Circumcision is the removal of the foreskin of the penis. The rite of circumcision (brit milah) is one of the most ancient practices of Judaism. The commandment to circumcise male children was given to Abraham in the Torah (Genesis 17:714 and repeated in Leviticus 12:3):
Circumcision is (in general) a common denominator among movements: Reform, Conservative, Reconstructionist, Orthodox all circumcise their male children and require male converts to undergo some form of circumcision.
Furthermore, faith is the only reason that Jews should circumcise their male children. In Moreh Nevuchim (Guide for the Perplexed), chapter 49, the Rambam says: "No one, however, should circumcise himself or his son for any other reason than pure faith; for circumcision is not like an incision on the leg or a burn on the arm, but a very difficult operation."
Current medical fashions play no role in circumcision, as it is a religious rite to Jews. Thus, it is pointless to attempt to argue for or against circumcision from a basis of medical need.
The circumcision is done the eighth day after birth, unless ill health or serious medical problems prevent it. Even Shabbat does not stop a Brit. If a child is not circumcised, he is still considered a Jew [San. 44a; Hoffmann, Melamed Lehoil, Yoreh Dea, #79]. However, if there are no medical contraindications (e.g., hemophilia), it is incumbent for the individual to arrange for their circumcision when medically safe to do so.
Traditionally, the father is supposed to perform the Brit. Since most fathers do not have the appropriate training, a specialist called a mohel is usually called upon to perform the circumcision. It is customary that, if possible, a mohel performs his first Brit on his own son-under the supervision of an experienced accredited mohel (his teacher). Mohelim are trained by all the religious movements and are sometimes also practicing physicians.
The operation is usually done in the home or the shul. The infant is surrounded by family and friends, and held by the sandek (an adult being honored by the parents, often a grandfather).
In the Ashkenazi community, on the Shabbat night (Friday night) prior to the Brit, the community comes to the home of the newborn to welcome him with singing and thanksgiving to Hashem on his birth, and a small meal is served including chickpeas (ar'bes). These are served as a sign of mourning: the child mourns that the angel caused him to forget everything he learned in his mother's womb (just one explanation of many for this custom of eating chickpeas).
In Sephardi communities, the night before the Brit is called the night of "Brit Yitzchak" and the community and family gather to learn the Zohar together, to sing special songs and have a dinner. In many places people from the community and family get together and study all night, not only on the night before the Brit, but also during the preceding week.