Egg shell quality and egg internal quality are of major importance to the egg industry worldwide. This review covers the formation of the hen’s egg and ways of measuring egg shell quality and egg internal quality. Egg shell quality may be measured as egg size, egg specific gravity, shell colour, shell breaking strength, shell deformation (destructive or non-destructive), shell weight, percentage shell, shell thickness, and shell ultrastructure. New methods emerge from time to time. Egg internal quality is measured as yolk colour, the integrity of the perivitelline membrane, and albumen quality. Factors that affect egg shell quality and egg internal quality are reviewed. The complexity of the process of egg shell formation means that imperfections can arise in a number of places in the oviduct of the hen. Egg shell quality may be affected by the strain and age of hen ; induced moult ; nutritional factors such as calcium, phosphorus, vitamins, water quality, non-starch polysaccharides, enzymes, contamination of feed ; general stress and heat stress ; disease, production system, or addition of proprietary products to the diets. Egg internal quality may be affected by storage ; hen strain and age ; induced moult, nutrition, and disease. An understanding of the range of factors that affect egg shell quality and egg internal quality is essential for the production of eggs of high quality.