The widespread practice of performing Kapparot with live chickens is subject to considerable debate and controversy. As Kapparot is not mentioned anywhere in the Talmud or early codes, there have been authorities throughout the ages who have tried to ban the practice - but to no avail. Additionally, it is noted that Kapparot resembles and possibly derives from ancient forms of witchcraft in which it was believed that one can transfer one's sins to an animal. As such, some authorities argue that Kapparot has no place in Jewish practice and should be dismissed, if not outright forbidden.
Other authorities defend the Kapparot ritual explaining that is not an exercise in magic, but rather, one of psychology. It is believed that declaring "this is my substitute, this is my atonement…" upon a chicken which is then slaughtered will arouse one to repentance which is certainly good preparation for Yom Kippur. The Rambam elaborates upon this idea further, suggesting that in the event that we are worthy of death due to our many sins, God in His mercy allows us the luxury of substituting an animal for slaughter, rather than to be slaughtered ourselves. Indeed, while performing Kapparot one should contemplate on the fragility of life and how one is constantly at God's mercy. Following the slaughter, the chicken should be donated to the poor for holiday consumption. The intestines, however, are given to the birds which is intended to symbolize our concern for both man and beast. Indeed, this reminds us that we are not only required to be merciful towards human beings, but such a requirement extends to all of God's creations.
The Ashkenazi approach to Kapparot considers it to be a minhag vatikin, a venerated practice that must not be neglected. Indeed, we are even taught to use a separate chicken for each and every family member. In keeping with the practice of the Arizal, many individuals perform kapparot in the early hours of Erev Yom Kippur following the selichot prayers, as such time is said to be one of Divine favor. Some authorities have compared performing kapparot to offering a sacrifice in the Beit Hamikdash. According to this approach, one should wait until at least the crack of dawn to perform kapparot in order to recall that sacrifices were never slaughtered in the Beit Hamikdash at night.
Others are not particular regarding when to perform kapparot and do so anytime between Rosh Hashana and Yom Kippur, and not necessarily on Erev Yom Kippur. Indeed, a number of authorities recommend performing kapparot promptly after Rosh Hashana so that the shochtim will not be under the pressure of having to slaughter a large number of chickens on Erev Yom Kippur. The long lines and rushed atmosphere which are typical of Erev Yom Kippur kapparot gatherings frequently lead to invalid slaughter and render the chickens, which are later distributed to the poor, as non-kosher.One should only use a shochet who is licensed by the municipal authorities to practice and who pays taxes on the income earned from slaughtering the kapparot.
A growing number of individuals prefer to use fish or even money as an alternative to chickens for kapparot due to instances of animal abuse with the use of live chickens. In fact, according to some authorities, the use of fish is to be preferred for kapparot over anything else. It is interesting to note that Rashi also used to perform kapparot but he didn’t use a chicken, fish, or money. He used flowers.
 Teshuvot Harashba 395, OC 605:1.
 Mateh Ephraim 605:5
 Chayei Adam 144:4.
 Rema, OC 605:1.
 Minhag Yisrael Torah, OC 583:6.
 Rema, OC 605:1.
 Magen Avraham 605:1.
 Mishna Berura 605:2, Rivevot Ephraim 8:236.
 Minhag Yisrael Torah 605:1.
 Pri Megadim 605; Elef Hamagen 605:2, Minhagei Eretz Yisrael (Gellis) 29:7.
 Aruch Hashulchan, OC 605:5; Mateh Ephraim 605:5.
 Mateh Ephraim 605:9.
 Elef Hamagen 605:11; Minhagei Eretz Yisrael (Gellis) 29:1.
 Shabbat 81b.