The oldest forms of customs duties were on exports and imports alike. They arose by analogy from the transit tolls which were customary in the middle use their fiscal importance was recognised, and it was easy from the standpoint of feudal politics to justify their continuance. Feudalism regarded every act of the vassal as the concern of the lord. If any vassal, or later any subject, found a new means of gain, feudalism imposed on him the duty of contributing a part thereof to the lord or the king. If a subject sold a commodity to a foreigner it seemed to the men of the middle ages that the king's interests were affected, and it seemed right that his permission should be paid for. The export duty is often a sort of compromise accepted for the removal of the prohibition of exportation. With the decay of the older, cruder, mercantile ideas and the advent of a period when national wealth came clearly to depend upon the size of national trade more than on its direction, export duties fell away. It is interesting to note in this connection that England retained until the middle of this century an export duty on coal, supposedly for the protection of her deposits from depletion. Turkey is now the only country where export duties form an important item of revenue. There the duty is 1 per cent of all exported commodities. Switzerland, Austria, Russia, and Italy have a few export duties upon products peculiar to their soil, the burden of which is supposed to fall upon the foreigner. France did away with them in 1881; Germany in 1873.

Import duties are still very numerous. As a branch of the taxes on consumption, their yield is very large. The German customs duties yield about 27 per cent of the total imperial receipts. Until recently, about half of the United States federal income was from this source ; now it is slightly less. The English customs duties yield 25 per cent of the gross receipts, the French 15 per cent, and the Italian the same.