The war split up families and scattered Spaniards far and wide
About 500,000 people whose families had to flee Spain during the civil war and the subsequent Franco era now have the right to apply for Spanish citizenship.
Spain's new Law of Historical Memory, enacted a year ago, applies to people whose mother or father was Spanish, and the grandchildren of those who fled.
They can start submitting applications for Spanish citizenship on Monday.
Most of those who qualify live in Argentina, Uruguay, Cuba, Chile, Venezuela, Mexico and France.
Nearly 300,000 Spanish descendants in Argentina are eligible for citizenship - the largest group, Spain's El Pais news website reports.
Descendants of Spaniards who left the country out of fear of political persecution or economic hardship between 1936 and 1955 can apply for nationality before 2011.
The Law of Historical Memory aims to compensate and rehabilitate victims of Spain's 1936-1939 civil war.
An estimated 500,000 people died in the war, which left Spain as a dictatorship under the rule of the fascist General Francisco Franco.
The country only began a transition to democracy after the death of Gen Franco in 1975.