Over 350 species of birds make up the order Psittaciformes; many of these are maintained in captive environments. Malnutrition is commonly diagnosed in captive psittacine birds; therefore, providing nutritionally adequate diets must be a primary concern. This review integrates quantitative information on the dietary habits and nutritional requirements of psittacine birds to facilitate the formulation and evaluation of diets for birds in captivity. Initially, characterization of the diet and feeding strategy of a particular species in the wild can provide insight into appropriate diet choices in captivity. Knowledge of the gastrointestinal anatomy and physiology can be used to elucidate the capacity of that species to utilize various feedstuffs. For example, the presence of a highly muscularized gizzard may allow a bird to utilize a seed-based diet, whereas a species possessing a small gizzard may be unable to process such a diet. Finally, nutrient requirements determined in a particular species or a related species (eg, similar digestive physiology and feeding strategy) may be applied to create a nutritionally adequate diet. Understanding the factors involved in selecting appropriate diets enables aviculturists, veterinarians, and nutritionists to maintain and propagate these birds with increased success.