The Internal Macedonian Revolutionary Organization (IMRO; Bulgarian: Вътрешна Македонска Революционна Организация (ВМРО), Vatreshna Makedonska Revolyutsionna Organizatsiya (VMRO); Macedonian: Внатрешна Македонска Револуционерна Организација, Vnatrešna Makedonska Revolucionerna Organizacija) was a revolutionary national liberation movement in the Ottoman territories in Europe, that operated in the late 19th and early 20th centuries.