The prohibition includes not eating any meat or dairy foods or their derivatives together, and not cooking any meat or dairy food together. Cooking refers to baking, frying, roasting, preparing, and so forth. The separation of meat and dairy foods in eating and cooking requires a complete separation of meat and dairy dishes, pots, silverware, utensils, dish sponges, dish towels, tablecloths, dishwashers, and small appliances in the kosher kitchen.

A caterer, restaurant, or other establishment can be supervised by a Rabbi and  certified kosher according to the Rabbi's standards.

For many processed and packaged foods, the presence of a hechsher is required to assure the kosher consumer of compliance with kashruth. It is not sufficient to rely on reading the ingredients on a label or package without a hechsher since:

• an ingredient may not be listed, especially if that ingredient is of minimal quantity
• a food processed in a factory where non-kosher products are prepared may have been prepared using non-kosher utensils or equipment
• processed foods may contain non-kosher chemical additives that are not readily identifiable to the consumer

Processed or packaged food products requiring a hechsher include:

• Bread
• Butter
• Cake
• Candy
• Canned vegetables and legumes
• Canned fish
• Cereal
• Cheese
• Cookies

• Imitation non-dairy products
• Meat
• Oil
• Pasta
• Smoked fish
• Soft drinks
• Spices
• Vegetable shortening
• Yogurt

Animals
A kosher animal chews its cud and has split hooves, including cows, goats, sheep, deer, bison, gazelle, antelope, ibex, addax and giraffe. Only the front part of the animal up to the end of the twelfth rib is considered kosher. The hind part of the animal contains prohibited nerves and fats that are difficult to remove.

Fowl
A kosher fowl is one that is not listed among the twenty-four types of fowl forbidden in the Bible and that is traditionally accepted as kosher, including chickens and domestic ducks, geese, turkeys, and doves.

Properly slaughtered and "koshered" animals and fowl
Kosher animals and fowl must be slaughtered according to the complex laws of shechitah (slaughtering) which proscribe the type of knife used, its sharpness, and the manner in which one performs the slaughter.

Kosher animals and fowl must be "koshered"--rinsed, soaked, salted and then triple-rinsed--within twenty-four hours of slaughtering to remove blood.

Dairy food
A kosher dairy food is a milk product from a kosher animal. A dairy food cannot contain any meat or non-kosher substances. Dairy foods include milk, butter, yogurt, cheese (hard or soft), cream cheese, and milk derivatives such as sodium caseinate and lactose.

Fish
Kosher fish have both fins and scales and include cod, flounder, haddock, halibut, herring, mackerel, pickerel, pike, salmon, trout, most tuna, and whitefish. Fish is not considered a meat or dairy food. It may be cooked with meat utensils for a meat meal, or with dairy utensils for a dairy meal. It may be served and eaten side by side with dairy foods. For a meat meal, fish must be served and eaten on a separate dish and with a separate utensil than a meat item.

Eggs
Eggs from any kosher fowl are kosher.

Pareve foods
Pareve foods are neutral, kosher foods that do not contain meat or dairy products. The following foods are pareve if they do not contain dairy or meat products: bread, cake, candy, cereal, cookies, crackers, soft drinks, tea, coffee, noodles, juice. All raw fruits, grains, vegetables, and kosher eggs are pareve.

Animals
Non-kosher animals include pigs, camels, horses, and donkeys.

Fowl
Non-kosher fowl are any listed among the twenty-four types of fowl forbidden in the Bible and that are not traditionally accepted as kosher, including wild ducks, geese, pigeons and doves.

Fish
Non-kosher fish include clams, crabs, lobster, oysters, shark, shrimp, squid, sturgeon, and swordfish.

Eggs
An egg from a non-kosher fowl is not kosher. A blood spot in any egg makes that egg unkosher.

Insects and rodents
Rodents, worms, amphibians, and creeping, swimming, or flying insects, are not kosher. Fruits, vegetables, or grains are not kosher when worms, insects, ants or mites are present on or in the item.