http://www.askmoses.com/en/article/564,18786/What-is-Kaparot.htmlIt is customary to perform the rite of Kaparot (symbolic “atonement”) on the day preceding Yom Kippur. Preferably, kaparot should be done in the early pre-dawn hours of the day before Yom Kippur. (If it is not possible to do so then, the rite may be performed earlier).
The custom of kaparot is an ancient one1, and was established as a reminder of the goat that the High Priest recited confession over on behalf of the Jewish People. That goat was sent to Azazel2. However, in order to ensure that the practice does not resemble a sacrifice in any way (since sacrifices are forbidden outside of the Holy Temple), a chicken is used -- since chickens were not offered on the altar.
The rite consists of taking a chicken -- a male takes a rooster and a female takes a hen -- and waving it over one's head three times while the appropriate text (found in the Siddur or Machzor) is recited. The fowl is then slaughtered in accordance with Halachic procedure. The monetary worth of the kaparot is given to the poor, or as is more popular today, the chicken itself is donated to a charitable cause.
We ask G-d that if we were destined to be the recipients of harsh decrees in the new year, may they be transferred to this chicken in the merit of this charity
If a chicken is unavailable, one may substitute other fowl or animals; many people use a Kosher live fish. Some give the actual fowl to the poor.
Others perform the entire rite with money, reciting the prescribed verses and giving the money to charity. There is no prescribed dollar amount; the donation should be according to one's financial abilities.Though the word kaparot means "atonement," one should not think that kaparot itself serves as a source of atonement. Rather, we ask G-d that if we were destined to be the recipients of harsh decrees in the new year, may they be transferred to this chicken in the merit of this charity. Furthermore, (many find the rite of kaparot very disturbing, and that is exactly the point), the mortality of the chicken should remind us of our own mortality and inspire us to correct our past and value our future.
[Even children, who are devoid of sin, do kaparot, since they, too, are sometimes the recipients of harsh heavenly decrees.]
Footnotes
1. The concept is found in the Talmud; see Talmud tractate Shabbat 81b Rashi "Hai Parpisa".
2. See Leviticus 16:8 ff.