World hunger continues to be a major problem. The main focus of those concerned with world hunger is on the availability of adequate calories for all, but this overshadows another problem: the availability of enough protein and enough dietary essential amino acids. We estimate that about a quarter of the world's population is getting barely enough protein; a particular issue is that of the essential amino acid lysine, which is deficient in cereal proteins, the biggest source of protein nutrition. Milk protein is an important source of dietary protein and is particularly rich in lysine and branched-chain amino acids. It accounts for 10% of all the global protein supply and provides the third highest supply after cereals and meat, but it is more important than the amounts would suggest because of its rich supply of essential amino acids and high digestibility (in contrast to cereal protein) and because of its acceptability to vegetarians. Global trade in dairy is still small (about 8% of dairy production is traded) but growing. Supplementation of cereal protein with milk protein has a potentially important role to play in balancing world protein nutrition.