The Portugal–Spain border, also referred to as "The Stripe", is one of the oldest geopolitical borders in the world. The current demarcation is almost identical to that defined in 1297 by the Treaty of Alcañices. The Portugal–Spain border is 1,214 km (754 mi) long, and is the longest uninterrupted border within the European Union, being free of border control since March 26, 1995, with a few temporary exceptions. The border is not defined for 18 km (11 mi) between the Caia river and Ribeira de Cuncos, because of the disputed status of Olivenza/Olivença, which has been disputed between the two countries for two hundred years.

Olivenza or Olivença is a town in southwestern Spain, close to the Portugal–Spain border. It is a municipality belonging to the province of Badajoz, and to the wider autonomous community of Extremadura.