Raul Prebisch was an Argentine economist who is known for his contributions to the field of development economics. Prebisch is best known for his theory of the "terms of trade," (the Prebisch-Singer hypothesis) which suggests that the prices of primary goods (such as raw materials) tend to decline relative to the prices of manufactured goods over time. This theory has been influential in shaping policy debates about trade and development, and it has been used to argue for policies such as import substitution (which promotes domestic production of goods that are normally imported) and export promotion (which encourages the export of goods to increase foreign exchange earnings).