The accepted custom is to perform a Berit Mila while the infant is positioned on a person’s lap, and the person on whose lap the Berit is performed is known by the term "Sandak." Different theories have been suggested to explain the etymology of the word "Sandak," one of which claims that it originates from the Roman word for a patron or father figure.

It is proper to assign the honor of Sandak to somebody who is God-fearing and committed to Torah, because he will be sitting alongside Eliyahu Ha’nabi at the Berit, and because the religious stature of the Sandak will have a beneficial spiritual effect upon the child’s soul. Indeed, the Rama (Rabbi Moshe Isserles of Cracow, 1525-1572), in his glosses to the Shulhan Aruch (Y.D. 264), writes that it is customary to try to select righteous men for the roles of Mohel and Sandak at a Berit Mila. This is mentioned as well by the Or Zarua (Rabbi Yishak of Vienna, 1180-1250), in Hilchot Mila. The Pele Yoetz (Rabbi Eliezer Papo, Bulgraria, 1786-1827) also writes that a righteous person should be chosen as Sandak as this will endow the young infant with holiness. It is told that Hacham Yaakob Musapi was especially insistent that both the Mohel and the Sandak should be righteous men. It is also told that Hacham Ovadia Sadka was once asked to identify the merit through which he was capable of achieving his great stature of piety, and he pointed to the fact that Rav Yosef Haim, the Ben Ish Hai, was the Sandak at his Berit. He humbly asserted that he did not deserve credit for his achievements, and that they actually fell short of what he was capable of achieving, and his stature was purely the product of having had such a towering Sadik as his Sandak.

Hacham Ovadia Yosef, in his work Yabia Omer (vol. 4, Siman 23), notes a ruling of the Hid"a (Rav Haim Yosef David Azulai, 1724-1807), cited in the name of the Kapot Temarim, of which many people are unaware. The Hid"a writes that the child’s father should verbally appoint the Sandak as his Shali’ah (agent), rather than just asking him to receive the honor. While it is well-known that the father must verbally appoint the Mohel as his Shali’ah to perform the Misva of Mila, many people are not aware that the father should also appoint the Sandak as his Shali’ah. The Hid"a explains that if the father appoints the Sandak as his Shali’ah, then when the Sandak performs the Misva he does so as the father’s agent, and thus the father receives great reward for the Misva. But if the father does not explicitly assign the Sandak as his Shali’ah, then the Misva is not credited to him, and he will not receive reward.

A person should endeavor to be a Sandak as many times as possible, in light of the great value and importance of this Misva. The Sandak’s legs at a Berit become like an altar upon which the child is placed as a kind of sacrifice, and this is an especially meaningful stature for one to obtain. One who serves as Sandak is rewarded with wealth, and this Misva also atones for sins involving the Berit. It is worthwhile even to incur great expenses for the sake of serving as Sandak, though under no circumstances should this Misva become a source of contention; one should not make a fight for the sake of being a Sandak. The Hid"a, in his work Abodat Ha’kodesh, writes that it is especially worthwhile to serve as Sandak during the weeks of Shobabim (the weeks when the first six Parashiyot of Shemot are read), as this is the period designated for correcting sins involving the Berit. He adds that there were those who would even offer a new father money to be able to serve as Sandak during these weeks. The Hazon Ish (Rabbi Avraham Yeshaya Karelitz, 1878-1953) cherished the Misva of being Sandak, and whenever he was asked to serve as Sandak he would joyfully announce that he is going to greet Eliyahu Ha’nabi. On one such occasion, the Berit was delayed and the Hazon Ish was forced to sit around and wait for a considerable amount of time for the Berit to begin. The family apologized to the sage for taking away time from his Torah studies, to which he responded, "Waiting to perform a Misva is also a Misva, and certainly waiting to be a Sandak is a Misva. You have nothing to apologize for."

The Midrash relates that when Abraham Abinu performed circumcision on himself and his household, he made a pile of severed foreskins. They were left out in the sun and quickly rotted, emitting a foul stench. The Midrash relates that the odor rose to the heavens and was greeted by the Almighty as though it was the fragrance of the Ketoret (incense) offered in the Bet Ha’mikdash, and an Ola sacrifice. This incident establishes a comparison of sorts between Berit Mila and the Ketoret and Ola offerings, and the Rabbis teach that specifically the Sandak is considered as having offered Ketoret.

Some have questioned the assertion that a Sandak is rewarded with wealth based on empirical evidence, as we see many people who serve as Sandak but are not wealthy. The Rebbe of Ger answered that this quality of the Misva applies only if the Sandak continues holding the baby throughout the entire ceremony, even during the recitation of the Berachot (which is, in fact, our community’s custom), and he drinks the wine. Rav Chaim Kreisworth (Antwerp, 1920-2002) testified that once he adopted the custom to hold the baby throughout the recitation of the Berachot, he received great material blessings.

Some have the custom that the Sandak recites the Berachot after the Berit.

There is also a custom that specifically the baby’s father places the child on the Sandak’s lap, because he is considered as offering a sacrifice upon the altar, which is represented by the Sandak. This is, indeed, the custom in our community.

Some communities observe a custom not to grant the honor of Sandak to the same individual for more than one son in the family. The basis for this custom is the fact that no Kohen would ever offer the Ketoret twice; because of the great value and significance of the Ketoret, no Kohen would offer Ketoret more than once, so that as many Kohanim as possible would have this privilege. Sepharadim, however, do not follow this custom, and may have the same person serve as Sandak for more than one child in a family.

The custom in our community is that the paternal grandfather is given the honor of Sandak for a couple’s first son, and the maternal grandfather receives this honor for the second. This is not required Halachically, but this is the generally accepted custom.

Some have the custom to invite a married man without children to serve as Sandak, as a "Segula" to help him and his wife have children.

Strictly speaking, even minors below the age of thirteen are allowed to serve as Sandak, but the accepted custom is not to give this honor to children under the age of thirteen. An unmarried man over the age of thirteen may be given the honor of Sandak.

Some communities have the custom to not allow the child’s father to serve as Sandak, as he will then have to recite the Beracha over the Mila while sitting, and it is questionable whether this Beracha may be recited while seated. Others, however, maintain that to the contrary, it is preferable for the father to himself serve as Sandak. In practice, our community allows the father to serve as Sandak. In fact, a father can theoretically serve as the Mohel and Sandak, and there are recorded incidents of Torah sages who performed Berit Mila while serving as Sandak.

It is proper for the Sandak to take a haircut and wear fine clothing, and immerse in a Mikveh, in honor of the Berit. It is customary for the Sandak to wear a Tallit during the Berit. If the Tallit belongs to him or his congregation, he recites the Beracha "Le’hit’atef Be’sisit" over the Tallit. Some have the custom that the Sandak does not work that entire day, as it is considered a Yom Tob for him.