The prohibition to eat meat and milk together is written 3 times in the Torah. Eating Kosher food constitutes one of the most important principles in Judaism.

"Of all the animals in the world, these are the ones that you may eat: Among mammals, you may eat [any one] that has true hooves that are cloven and that bring up its cud. However, among the cud-chewing, hoofed animals, these are the ones that you may not eat: The camel... The hyrax... The hare... The pig... Do not eat the flesh of any of these animals...

This is what you may eat of all that is in the water: You may eat any creature that lives in the water, whether in seas or rivers, as long as it has fins and scales. All creatures in seas and rivers that do not have fins and scales... must be avoided by you... You must avoid them by not eating their flesh...

These are the flying animals that you must avoid...
Every flying insect... shall be avoided by you...
Every animal that walks on its paws... shall be unclean to you...
These are the smaller animals... which are unclean to you...
Every small animal that breeds on land shall be avoided...

[With this law, you will be able] to distinguish between the unclean and the clean, between edible animals and animals which may not be eaten."
Vayikra (Leviticus) 11:1-47

"Do not eat any abomination... You may thus eat every animal that has a true hoof that is cloven into two parts, and which brings up its cud... There are some [animals] that you may not eat. These include the camel, hyrax and hare... Also included is the pig... Do not eat the flesh of these [animals] and do not touch their carcasses.

Among that which is in the water, you may eat anything that has fins and scales. But those which have no fins and scales, you may not eat, since they are unclean to you.
You may eat every kosher bird... Every flying insect that is unclean to you shall not be eaten... You may not eat any [mammal or bird] that has not been properly slaughtered."
Dvarim (Deuteronomy) 14:3-21

How do I know it's Kosher?

The Hebrew word "Kosher" means fit or proper as related to dietary (kosher) laws. It means that a given product is permitted and acceptable. Though hygienic and health benefits have been attributed to the observance of kashrut, their ultimate purpose and rationale is simply to conform to the mitzvot (commandments) as expressed in the Torah.

KOSHER AND NON-KOSHER MEAT, POULTRY, AND FISH

1. Meat:
The Torah lists the characteristics of permitted mammals and fish, and enumerates the forbidden fowl. The only mammals permitted are those which chew their cud (ruminants) and are cloven hoofed.

2. Poultry:
The Torah enumerates 24 forbidden species of fowl. The Shulchan Aruch states that we may eat only those birds for which there is an established tradition that the bird is kosher.

3. Fish:
The Torah establishes two criteria in determining kosher fish. They must have fins and scales (skin of the fish). All shellfish are prohibited. One should not eat fish with meat.

KOSHER SLAUGHTERING (Shechita)

The processing of kosher meats and poultry requires that the animal be slaughtered in the manner prescribed by the Torah.

1. Shechita:
Only a trained kosher slaughterer (shochet) is qualified to slaughter an animal. The trachea and esophagus of the animal are severed with a special razor-sharp, perfectly smooth blade causing instantaneous death with no pain to the animal.

2. Bedika:
After the animal has been properly slaughtered, a trained inspector (bodek) inspects the internal organs for any physiological abnormalities that may render the animal non-kosher (treif). The lungs in particular, must be examined to determine that there are no adhesions (sirchot) which may be indicative of a puncture in the lungs. If an adhesion is found, the bodek must examine it carefully to determine its kashruth status.

3. Glatt Kosher:
Though not all adhesions will necessarily render an animal tref, some Jewish communities or individuals only eat of an animal that has been found to be free of all adhesions. "Glatt" literally means smooth, indicating that the meat comes from an animal whose lung has been found to be free of all adhesions. Of late "Glatt Kosher" has come to be used more broadly as a consumer phrase meaning kosher without question.

4. Nikkur:
There are special cutting procedures for beef, veal and lamb, called "Nikkur" in Hebrew. Many blood vessels, nerves, and lobes of fat are forbidden and must be removed before, a costly and time-consuming procedure.

5. Koshering:
The Torah forbids the eating of the blood of an animal. The two methods of extracting blood from meat are salting and broiling. Because of the preponderance of blood in the liver, it can only be koshered through broiling. Meat once ground cannot be made kosher, nor may meat be placed in hot water before it has been "koshered".

MEAT AND MILK IN THE KOSHER KITCHEN

The Torah forbids cooking meat and milk together in any form, eating such cooked products, or deriving benefit from them. As a safeguard, the Rabbis extended this prohibition to disallow the eating of meat and dairy products at the same meal or preparing them on the same utensils. One must wait up to six hours after eating meat products before any dairy products may be eaten. However, meat may be eaten following dairy products with the one exception of hard cheese (6 months old or more), which also requires up to a six hour interval. Prior to eating meat after dairy, the mouth must be rinsed.

1. Utensils:
The Kosher kitchen must have two separate sets of utensils, one for meat and poultry and the other for dairy foods. There must be separate, distinct sets of pots, pans, plates and silverware.

2. Washing Dishes:
In a sink used for both meat and milk dishes and products, dishes and utensils must be placed or washed on a rack. Separate racks are to be used for meat and dairy use.

EGGS:

The eggs or animal by-product of non-kosher birds or fish are not kosher. Caviar, therefore, must come from a kosher fish. Eggs of kosher fowl which contain a bloodspot must be discarded, and therefore eggs should be checked before use.

BAKERIES, BAKED GOODS, BREAD, ROLLS, PASTRIES AND BAGELS

1. The "Taking" of Challah:
The Torah requires that a portion of every batter of dough prepared for baking be set aside as "Challah". The Challah portion taken may be of any size and is to be burned. This ritual is obligated only when the dough is of Jewish ownership and is made from the flour of five grains: wheat, oats, rye, spelt, and barley. When the flour used is a blend with other types of flour, such as corn or rice, a Rabbinic authority is to be consulted.

If this Mitzvah has not been performed in the bakery, it may be performed in the home by placing all the baked goods in one room, breaking open all sealed packages material, and removing and burning a small piece from one of the loaves. When some of the loaves are of wheat flour and some of the loaves are of rye (or one of the five previously listed grains). Challah must then be taken from a loaf of each type.

2. Emulsifiers, Shortenings, Oils, Flavors, Fillings, Cremes, and Fudges:
The Kosher status of a product containing any of these ingredients can only be verified by reliable Kosher certification.

3. Cake, Pastries, Doughnuts, & Dairy Breads:
These products should be considered non-kosher unless certified Kosher.

DAIRY PRODUCTS

1. Chalav Israel:
A Rabbinic law requires that there be supervision during the milking process to ensure that the source of the milk is from a kosher animal.

2. Cheeses, Sour Cream, Buttermilk, Yogurt, & Desserts:
All these products require Kashruth certification. Rennet is used in their production as a curdling and coagulating ingredient. The use of non-kosher rennet, renders the product non-kosher.

3. Margarine:
Margarine usually contains glycerites and therefore requires rabbinic certification. Also, unless the margarine is marked Pareve, it should be considered dairy.

NATURAL AND HEALTH FOODS

Even if a product is sold in a natural or health food store, it requires supervision.

WINES AND GRAPE PRODUCTS

All grape wines or brandies must be prepared under strict Orthodox Rabbinic supervision. Once the wine has been cooked, no restrictions are attached to its handling. Grape Jam, Grape Jelly, Natural and "Artificial" Grape Flavors, can be used only when produced under proper kosher supervision. Liqueurs, even though not possessing a wine base, nevertheless require supervision because of the flavorings used in these products.

TRAVELING KOSHER

When traveling by plane, train, or ship, kosher meals should be ordered in advance. These meals are heated in non-kosher ovens. The traveler can ascertain by the intact kashrut certification seals that the dinners have not been tempered with. Any dinner which is not so sealed should not be eaten.