From the point of view of the Shia' Law (Fiqh) the condition for meat to be sold in a halal (permissible) way in the marketplace, meat shops, and stores (supermarkets) is that first of all: The meat must  have come from halal animals (animals that are permissible to eat according to Islamic law). Second of all: This animal meat (that is halal) must have been slaughtered according to Islamic laws. In order to fulfill the proper Islamic laws of slaughtering, the conditions below must be followed:
1) The butcher must be a Muslim, or someone who is ruled as a Muslim; like a Muslim child who has not reached the age of puberty yet.[1] And the slaughtering by a non-Muslim person is according to the ruling of a dead animal (above example). In this case there is no difference between a disbeliever of the Book or a disbeliever who is not a Person of the Book. [2]
2) The head of the animal must be cut with something made from iron.
3) At the same time of cutting the head (slaughter) the front of the body of the animal must be facing in the direction of Qibla (Mecca, Saudi Arabia).
4) At the same time of the slaughter, the butcher must say the Name of God on his or her tongue out loud. 5) After the animal has been slaughtered, it must show a few small bodily movements until it is obvious that it was recently alive and now is killed completely.
6) The animal should not be slaughtered from the back of the head (behind the head.) [3]
If all of these conditions are met during the slaughter of an animal, its meat is halal (allowed/ permissible) and can be lawfully used (eaten).
But the Sunnis [4] (except among them the Hanbalis who are in agreement with the Shia's) have a different opinion regarding this issue. They say that meat that was slaughtered by the hand of a disbeliever (Kufar) that is NOT a Person of the Book (Christian or Jew) is not halal. And from this viewpoint they do not differ from the Shia's. But eating the slaughtered meat of the disbelievers who are People of the Book is halal to eat. [5] But a Shia' can not act according to their school of thought! The responsibility of Shia's (according to Islamic laws) is to act according to the laws of the Ahl al-Bayt (Family of the Prophet).

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