The Lanka Sama Samaja Party (literally Lanka Equal Society Party, in Sinhala: ලංකා සම සමාජ පක්ෂය, in Tamil: லங்கா சமசமாஜக் கட்சி) is a Trotskyist political party in Sri Lanka. The party was founded in 1935 and emerged as a major political force in the Sri Lankan independence movement during the 1940s. It joined a coalition government in 1964, and was then expelled from the Fourth International. It peaked in political strength in the 1970s, but has declined gradually during the last 30 years.