The Internal Macedonian Revolutionary Organization (IMRO) is a revolutionary national liberation movement in the Ottoman territories in Europe, that operatesin the late nineteenth and early twentieth centuries.

Founded in 1893 in Salonica, initially its aim is to gain autonomy for Macedonia and Adrianople regions in the Ottoman Empire, however later it becomes an agent serving Bulgarian interests in Balkan politics.

IMRO group models itself after the Internal Revolutionary Organization of Vasil Levski and accepts its motto "Freedom or Death" .

Starting in 1896 it fights the Ottomans using guerrilla tactics, and in this they are successful, even establishing a state within state in some regions, including their own tax collectors. \

This effort escalates in 1903 into the Ilinden–Preobrazhenie Uprising.

The fighting involves about fifteen thousand IMRO irregulars and forty thousand Ottoman soldiers

After the uprising fails, and the Ottomans destroy some hundred villages, the IMRO resorts to more systematic forms of terrorism targeting civilians.

During the Balkan Wars and the First World War the organization supports the Bulgarian army and joins to Bulgarian war-time authorities when they temporarily take control over parts of Thrace and Macedonia.

In this period autonomism as a political tactic is abandoned and annexationist positions are supported, aiming for eventual incorporation of occupied areas into Bulgaria.

After the First World War the combined Macedonian-Thracian revolutionary movement separates into two detached organizations, IMRO and ITRO.

After this moment the IMRO earns a reputation as an ultimate terror network, seeking to change state frontiers in the Macedonian regions of Greece and Serbia (later Yugoslavia).

They contest the partitioning of Macedonia and launch aids from their Petrich stronghold into Greek and Yugoslav territory.

Their base of operation in Bulgaria is jeopardized by the Treaty of Niš, and the IMRO reacts by assassinating Bulgarian prime minister Aleksandar Stamboliyski in 1923, with the cooperation of other Bulgarian elements opposed to him.

In 1925 the Greek army launches a cross-border operation to reduce the IMRO base area, but it is ultimately stopped by the League of Nations, and IMRO attacks resume.

In the interwar period the IMRO also cooperates with the Croatian Ustaše, and their ultimate victim is Alexander I of Yugoslavia, assassinated in France in 1934.

After the Bulgarian coup d'état of 1934, their Petrich stronghold is subjected to military crackdown by the Bulgarian army, nd the IMRO is reduced to a marginal phenomenon

The organization changes its name on several occasions.

After the fall of communism in the region, numerous parties claim he IMRO name and lineage to legitimize themselves.

Among them, in Bulgaria a right-wing party carrying the prefix "VMRO" will be established in the 1990s, while in the Republic of Macedonia a right-wing party will be established under the name "VMRO-DPMNE".