Two goods that "go together," either in consumption or production. In terms of demand, a complement-in-consumption is one of two goods that are consumed together such that an increase in the price of one good leads to a decrease in demand and a leftward shift in the demand curve for the other good. If the demand of good 1 decreases as the price of good 2 increases, the goods are complements-in-consumption. In terms of supply, a complement-in-production is one of two goods that are produced jointly using the same resources, such that an increase in the price of one good leads to an increase in supply and a rightward shift in the supply curve for the other good. If the supply of good 1 increases as the price of good 2 increases, the goods are complements-in-production.