The Committee of Union and Progress (CUP) (اتحاد و ترقى جمعيتی), later the Union and Progress Party (اتحاد و ترقى فرقهسی), was a secret revolutionary organization and political party active between 1889 and 1926 in the Ottoman Empire and the Republic of Turkey. The foremost faction within the Young Turk movement, it instigated the 1908 Young Turk Revolution, which ended absolute monarchy and began the Second Constitutional Era. From 1913 to 1918, the CUP ruled the empire as an authoritarian one-party state and committed genocides against the Armenian, Greek, and Assyrian peoples as part of a broader policy of ethnic erasure during the late Ottoman period. The CUP was associated with the wider Young Turk movement, and its members have often been referred to as Young Turks, although the movement produced other political parties as well. Within the Ottoman Empire its members were known as İttihadcılar ('Unionists') or Komiteciler ('Committeemen').
Beginning as a liberal reform movement, the organization was persecuted and forced into exile by the Ottoman sultan Abdul Hamid II's autocratic government because of its calls for democratization, secularization, and reform in the empire. Inspired by revolutionary groups such as the Armenian Revolutionary Federation and Internal Macedonian Revolutionary Organization, the CUP had developed into a clandestine revolutionary group by 1906, infiltrating Ottoman army contingents based in Rumelia which were fighting ethnic insurgents in the Macedonian Struggle. In 1908, the Unionists forced Abdul Hamid to reinstate the Ottoman Constitution in the Young Turk Revolution, ushering in an era of political plurality. Mehmed Talât established himself as the leader of the CUP after the revolution, and it developed into a political party following a Turkish nationalist ideology known as İttihadism. Its main rival was the Freedom and Accord Party, another Young Turk party which called for the federalization and decentralization of the empire, in opposition to the CUP's desire for a centralized and unitary Turkish-dominated state.