The Asiento de Negros (agreement of blacks') was a monopoly contract between the Spanish Crown and various merchants for the right to provide African slaves to colonies in the Spanish Americas. The Spanish Empire rarely engaged in the trans-Atlantic slave trade directly from Africa itself, choosing instead to contract out the importation to foreign merchants from nations more prominent in that part of the world; typically Portuguese and Genovese, but later the Dutch, French and British.

The Asiento did not concern French or British Caribbean but Spanish America. The 1479 Treaty of Alcáçovas divided the Atlantic Ocean and other parts of the globe into two zones of influence, Spanish and Portuguese. The Spanish acquired the west side washing South America and the West Indies, whilst the Portuguese obtained the east side washing the west coast of Africa - and also the Indian Ocean beyond. The Spanish relied on African slave labour to make their American colonial project possible, but now lacked any trading or territorial foothold in West Africa, the principal source of slave labour. Thus the Spanish were reliant on Portuguese slave traders for all their requirements.