Forages have historically been used as feed for animals, both livestock and wildlife. Studying forages without looking into their use within livestock systems would be less useful. The different types of livestock operations use forages differently to reach their specific goals. Dairy farms want maximum milk production, beef operations want the desired meat to sell in a demanding market, sheep operations may want meat or wool production. Feeding all these types of animals must be done differently. The growth stage of the animal is often the key to diets. What does each animal require at each stage to be productive? Which forage will best supply what is needed in the most economical and environmentally friendly way? An understanding of forages, livestock nutritional needs, and economics is needed.