The Social Democratic Party of Lithuania (Lithuanian: Lietuvos socialdemokratų partija LSDP) is a social-democratic political party in Lithuania. It is the longest-existing party in Lithuania having been founded as an underground Marxist organization in 1896. During the period of Soviet occupation the party was forced into exile emerging once again in Lithuania in 1989.The party’s president since 2009 is Algirdas Butkevičius.