The Orange Free State (Dutch: Oranje Vrijstaat; Afrikaans: Oranje-Vrystaat;) was an independent Boer sovereign republic under British suzerainty in Southern Africa during the second half of the 19th century, which ceased to exist after it was defeated and surrendered to the British Empire at the end of the Second Boer War in 1902. It is one of the three historical precursors to the present-day Free State province.

Extending between the Orange and Vaal rivers, its borders were determined by the United Kingdom of Great Britain and Ireland in 1848 when the region was proclaimed as the Orange River Sovereignty, with a British Resident based in Bloemfontein. Bloemfontein and the southern parts of the Sovereignty had previously been settled by Griqua and by Trekboere from the Cape Colony.

The Voortrekker Republic of Natalia, founded in 1837, administered the northern part of the territory through a landdrost based at Winburg. This northern area was later in federation with the Republic of Potchefstroom which eventually formed part of the South African Republic (Transvaal).

Following the granting of sovereignty to the Transvaal Republic, the British sought to drop their defensive and administrative responsibilities between the Orange and Vaal rivers, while local European residents wanted the British to remain. This led to the British recognising the independence of the Orange River Sovereignty and the country officially became independent as the Orange Free State on 23 February 1854, with the signing of the Orange River Convention. The new republic incorporated the Orange River Sovereignty and continued the traditions of the Winburg-Potchefstroom Republic.

The Orange Free State was annexed as the Orange River Colony in 1900. It ceased to exist as an independent Boer republic on 31 May 1902 with the signing of the Treaty of Vereeniging at the conclusion of the Second Boer War. Following a period of direct rule by the British, it attained self-government in 1907 and joined the Union of South Africa in 1910 as the Orange Free State Province, along with the Cape Province, Natal, and the Transvaal. In 1961, the Union of South Africa became the Republic of South Africa.

The Republic's name derives partly from the Orange River, which was named by the Dutch explorer Robert Jacob Gordon in honour of the Dutch ruling family, the House of Orange, whose name in turn derived from its partial origins in the Principality of Orange in French Burgundy. The official language in the Orange Free State was Dutch.