The Republican Union (Spanish: Unión Republicana) was a Spanish republican party founded in 1934 by Diego Martinez Barrio.

It was formed as a result of a merger of several small republican parties, most notably Diego Martinez Barrio's Radical Democratic Party and the Radical Socialist Republican Party, both of which had split away from the more moderate Radical Republican Party of Alejandro Lerroux.

Integrated in the Popular Front ahead of the 1936 election, the party won 38 seats becoming the fourth largest party. It formed a governing coalition with Manuel Azaña's Republican Left. Though it participated in all republican governments during the Spanish Civil War, it played a minor role starting under Largo Caballero's government.

In exile in Mexico, it was the main support of the Republican government-in-exile until it was dissolved in 1959 to found the Spanish Democratic Republican Action along with the Republican Left.

• Republican Union (Spain, 1893)
• Republican Union Party (Spain)

• Nigel Townson. The Crisis of Democracy in Spain: Centrist Politics Under the Second Republic, 1931-1936. Sussex Academic Press. 2000. pp. 2–3.
• Beevor, Antony. The Battle for Spain. The Spanish Civil War 1936-1939. Penguin Books. 2006. p. 456.