The Treaty of Tordesillas, signed in Tordesillas, Spain on 7 June 1494, and authenticated in Setúbal, Portugal, divided the newly-discovered lands outside Europe between the Portuguese Empire and the Spanish Empire (Crown of Castile), along a meridian 370 leagues west of the Cape Verde islands, off the west coast of Africa. That line of demarcation was about halfway between the Cape Verde islands (already Portuguese) and the islands entered by Christopher Columbus on his first voyage (claimed for Castile and León), named in the treaty as Cipangu and Antilia (Cuba and Hispaniola).

The lands to the east would belong to Portugal and the lands to the west to Castile. The treaty was signed by Spain, 2 July 1494, and by Portugal, 5 September 1494. The other side of the world was divided a few decades later by the Treaty of Zaragoza, signed on 22 April 1529, which specified the antimeridian to the line of demarcation specified in the Treaty of Tordesillas. Originals of both treaties are kept at the General Archive of the Indies in Spain and at the Torre do Tombo National Archive in Portugal.

Despite considerable ignorance regarding the geography of the so-called New World, Portugal and Spain largely respected the treaty. The other European powers however did not sign the treaty and generally ignored it, particularly those that became Protestant after the Reformation. Similarly, the Indigenous nations did not acknowledge the treaty, and as the legal foundation for the Discovery Doctrine, it has been a source of ongoing tension regarding land ownership into modern times, cited as recently as the 2005 United States Supreme Court case Sherrill v. Oneida Nation.