Ingested lipids undergo intestinal emulsification, digestion, micellar solubilization, cell membrane permeation, intracellular esterification and incorporation into lipoproteins before release to the interstitial fluid. Bile salts secretion, essential to both emulsification and micelle formation in the intestine, has been found to be influenced by quantity and quality of dietary lipids and by other emulsifiers. Modifications of dietary lipid contents cause changes in pancreatic lipase content and secretion. Colipase secretion by the pancreas seems dependent on both lipid and protein intakes. Intracellular processes essential for lipid absorption increases in rate as lipid intake increases. Bile salts seem to play important roles as moderators of these processes. The ability to digest lipids is not fully developed in the newly hatched poultry. Addition of bile salts, lipase or phospholipids to chick diets improves the digestibility of animal fats, demonstrating that lipid digestive processes are not fully functional in the very young. Physiological studies support these indications. Lipase concentration in pancreatic tissue and intestinal contents of poultry increases several-fold during the first few weeks after hatch. Similar changes with age have been observed in bile salt secretion. The development in enterocytes of fatty acid-binding protein activity seems to parallel the development in lipase activity and bile salt secretion in poultry.