The Arab Socialist Baʿath Party (Arabic: حزب البعث العربي الاشتراكي Ḥizb al-Baʿath al-ʿArabī al-Ishtirākī [ˈħɪzb alˈbaʕθ alˈʕarabiː alʔɪʃtɪˈraːkiː]) was a political party founded in Syria by Mishel ʿAflaq, Ṣalāḥ al-Dīn al-Bītār, and associates of Zaki al-ʾArsūzī. The party espoused Baʿathism (from Arabic بعث baʿath meaning "renaissance" or "resurrection"), which is an ideology mixing Arab nationalist, pan-Arabism, Arab socialist, and anti-imperialist interests. Baʿathism calls for unification of the Arab world into a single state. Its motto, "Unity, Liberty, Socialism", refers to Arab unity, and freedom from non-Arab control and interference.

The party was founded by the merger of the Arab Baʽath Movement, led by ʿAflaq and al-Bitar, and the Arab Baʽath, led by al-ʾArsūzī, on 7 April 1947 as the Arab Baʿath Party. The party quickly established branches in other Arab countries, although it would only hold power in Iraq and Syria. The Arab Baʿath Party merged with the Arab Socialist Movement, led by Akram al-Hawrani, in 1952 to form the Arab Socialist Baʿath Party. The newly formed party was a relative success, and it became the second-largest party in the Syrian parliament in the 1954 election. This, coupled with the increasing strength of the Syrian Communist Party, led to the establishment of the United Arab Republic (UAR), a union of Egypt and Syria, in 1958. The UAR would prove unsuccessful, and a Syrian coup in 1961 dissolved it.

Following the break-up of the UAR, the Baʿath Party was reconstituted. However, during the UAR period, military activists had established the Military Committee that took control of the Baʿath Party away from civilian hands. In the meantime, in Iraq, the local Baʽath Party branch had taken power by orchestrating and leading the Ramadan Revolution, only to lose power a couple of months later. The Military Committee, with Aflaq's consent, took power in Syria in the 8th of March Revolution of 1963.

A power struggle quickly developed between the civilian faction led by ʿAflaq, al-Bitar, and Munīf ar-Razzāz and the Military Committee led by Salah Jadid and Hafez al-Assad. As relations between the two factions deteriorated, the Military Committee initiated the 1966 Syrian coup d'état, which ousted the National Command led by al-Razzāz, ʿAflaq, and their supporters. The 1966 coup split the Baʿath Party between the Iraqi-dominated Baʿath movement and the Syrian-dominated Baʿath movement.