Socialist Vanguard Party (in French: Parti de l'Avant-Garde Socialiste) founded in 1966. The party was led by El Hachemi Chérif. Although not legally recognized, it has persisted as a political opposition party throughout the single-party period in Algeria. As an outgrowth of the Algerian Communist Party (Parti Communiste Algérien), which disappeared soon after Algerian independence, the PAGS has consistently opposed the government, offering sharp criticism of all political leaders and most of their programs. Its members, referred to as "Pagsistes", had infiltrated almost every legally recognized mass association despite their unofficial status. The Pagsistes were especially prominent in such organizations as the UNJA and UGTA, encouraging leftist tendencies.
The PAGS coalition relationship with the regime ended when Chadli Benhadid came to power, who sought to purge pagistes from positions of power within the state-party apparatus, and moved toward economic liberalization.
The party was legalized in 1989.
In 1993, PAGS was reconstructed as Ettehadi. A group who wanted to retain the communist legacy of the party broke away and formed the Algerian Party for Democracy and Socialism. During the Algerian Civil War, Ettehadi strongly opposed the Islamists and supported the banning of FIS.
In 1999, Ettehadi was reconstructed as the Democratic and Social Movement (Mouvement Démocratique et Social).