Egg shell quality and egg internal quality are of major importance to the egg industry worldwide and may be measured in a range of ways both commercially and in research facilities. Egg quality is influenced by a range of factors including strain of bird, age of bird, nutrition, moult status, water quality, general stress, heat stress, disease, housing, production system, environmental contaminants and use of proprietary products designed to improve egg quality. Improved understanding of the way in which the egg and egg shell are formed, including knowledge of the proteins comprising the organic matrix of the shell has assisted with diagnosis of the causes of egg shell quality problems and with genetic selection for good quality. Ongoing technological advances have led to improved in-line monitoring of egg shell quality. Egg quality is also important for food safety as eggs are periodically implicated in cases of food-borne illness.