Internal Dobrujan Revolutionary Organisation

The Internal Dobrujan Revolutionary Organisation (Bulgarian: Вътрешна добруджанска революционна организация; Romanian: Organizaţia Internă Revoluţionară Dobrogeană), IDRO, was a Bulgarian nationalist and revolutionary organisation active in Romanian Dobruja from 1923 to 1940. It was labeled 'a terrorist organization' by the Romanian government, though in Bulgaria it was regarded as a liberation movement.

The organisation was founded in 1923 under the leadership of Docho Mihaylov and on the basis of the Great Convention of Dobruja (bulg. Велик добруджански събор), a Bulgarian political organisation established in 1919 to fight against the transfer of Southern Dobruja to Romania. The IDRO detachments fought against the wide-spread brigandage in the region, as well as the Romanian administration in the region. Like the Internal Macedonian Revolutionary Organisation in Macedonia and the Internal Thracian Revolutionary Organisation in Thrace, IDRO demanded political autonomy of Dobruja under the mandate of the League of Nations.

In 1925, a left wing named Dobrujan Revolutionary Organisation (Bulgarian Добруджанска революционна организация) seceded from the organisation under the influence of the Bulgarian Communist Party. This wing militated for a independent Republic of Dobruja, which would either be part of a "Federative Republic of the Balkans" or to become a Republic of the Soviet Union.

The division of IDRO significantly hampered the work of the organisation, although it continued its activity under different forms until 1940 when Southern Dobruja was restored to Bulgaria under the terms of the Treaty of Craiova.