Originally, the Jewish firstborn were the sanctified priestly class. They were inducted into G‑d's service when they were spared from the Plague of the Firstborn that struck Egypt. However, when the Jews – firstborn included – served the Golden Calf, the firstborn forfeited their status. The priesthood was transferred to the tribe that did not participate in the Golden Calf hoopla—the Levites, and particularly the children of Aaron.

Ever since, all male Israelite firstborn must redeem themselves in a pidyon haben ceremony from a descendant of Aaron, a.k.a a kohen.

Who:

Any male who is a firstborn to his mother. Exceptions include:

1. If either parent is the child of a kohen or Levite

2. C-section babies.

If the parents don't redeem their child, then upon reaching adulthood, he must do it himself3. If the mother miscarried before the birth of this child—consult a rabbi.

If the parents don't redeem their child, then upon reaching adulthood, he must do it himself.

When:

On the child's 31st day. Already past? Then ASAP.

Sephardic Jews schedule the ceremony for the eve of the 31st day, Ashkenazim for the afternoon of the 31st day.

What if that day falls on Shabbat or a major Jewish holiday? Then hold the ceremony the next night or day.

How:

The Torah sets the price at five shekalim, approximately 100 grams of silver.

Traditionally, the mitzvah is performed during a "mitzvah meal" attended by family and some friends. After the meal has started, the firstborn is brought in on an elaborate silver tray adorned with jewelry.

"My Israelite wife has borne me this firstborn son," the father tells the designated kohen.

The father and the kohen then have a brief scripted dialogue, at the conclusion of which the father gives the redemption money and recites a special blessing. The kohen then recites a blessing over a cup of wine.

Our sages say that partaking of the pidyon haben meal has the same spiritual benefit as does fasting for 84 days! That's why it's a tradition to serve packets of sugar and garlic—food that goes a long way for a long time.