Barisan Sosialis (English: Socialist Front) was a political party in Singapore. It was formed on 29 July 1961 and officially registered on 13 August 1961 by left-wing members of the People's Action Party (PAP) who had been expelled from the PAP. The prominent founding members of the Barisan were Lee Siew Choh and Lim Chin Siong. It became the biggest opposition party in Singapore in the 1960s and the 1980s.