Assiento (Sp. asiento, treaty), a term used to designate the treaties made by Spain with foreign countries for the supply of negro slaves to her South American provinces. The Spanish government, having no settlements on the African coast, encouraged adventurers to supply slaves by securing to them a monopoly of the trade, with other commercial privileges. The Flemish merchants received the contract from Charles V.; Philip II. gave it to the Genoese, under whose title the traffic was chiefly carried on by British traders; and Philip V. to a French company. The terms of this last assiento were the privilege of sending a ship of 500 tons with merchandise free of duty to Spanish America, and the payment of a sum on each imported negro, the minimum number of slaves being fixed at 4,800 annually. This contract was transferred by the same king to the South sea company, but abrogated shortly after at the peace of Aix-la-Chapelle. It never gave satisfaction to Spain; and the contractors always lost money, their local factors and agents reaping the profits.