Pets need to eat various nutrients in order to keep them healthy. These can be provided from a wide range of ingredients. The skill of a petfood manufacturer is in selecting and blending various cuts of meat, fish, vegetables, cereals, minerals and vitamins to produce nutritionally balanced foods that pets enjoy. 

The key factors are:
• Nutritional value, quality and palatability of the individual ingredients
• How the ingredients and nutrients are combined (some can bind together so they become unavailable)
• The cooking process

All of these factors affect the overall nutritional balance.
There is a huge variety of petfoods available to pet owners but they all aim to meet the pet’s nutritional needs. Pet owners will generally choose food on the basis of how much it costs, whether their pet likes it or not, and according to their own interpretation of what their pet will enjoy.

Pet foods can be classified into two groups:
Complete: nutritionally complete, providing all the nutrients in the amounts and proportions the pet needs. Complementary: These foods are designed to be a part of the diet; however they do not meet the known nutritional requirements when fed alone so they must be fed along with an additional food type such as mixer biscuits in the case of the dog, or hay, in the case of rabbits. All complementary foods are labelled as such with appropriate feeding guidelines.

Making a suitable food for a pet at home is time consuming, demanding and requires a level of knowledge about nutrition that is difficult to acquire.

There is a huge body of information about pet nutrition which has been developed over many years. Among the many thousands of publications and papers, a key source of nutritional information for pet food manufacturers are the National Research Council Guidelines published by the US National Academy of Sciences. These guidelines detail the basic nutritional requirements of cats and dogs and give clear guidance on the essential nutrients required by the different animals.

The European Pet Food Manufacturers' Association, FEDIAF, have also produced a nutritional guideline, which is a comprehensive review of the data produced as a practical guide for manufacturers. FEDIAF is in the process of updating their publication to incorporate the latest published information on dog and cat nutrient requirements. In the US, the Association of American Feed Control Officials produce a yearly publication which seeks to provide practical guidelines for the pet food industry in America.