| Sèvres, Treaty of | Süleyman Nuri (1895-1966) | 
| Sült, Wilhelm (1888-1921) | Sachithanandam, Vallipuram (1913-1977) | 
| Sachs | Safarov, G.I. (1891-1942) | 
| Saint-Germain, Treaty of | Saint-Simon, Comte (1760-1825) | 
| Sakharov, Andrei (1921-1989) | Saklatvala, Shapurji (1874-1936) | 
| Salandra, Antonio (1853-1931) | Salih Hacioglu (1880-1954) | 
| Salles | Samarakkody, Edmund Peter (1912– 1992) | 
| Samoilova, Konkordia Nikolaevna (1876-1921) | Samuel, Raphael (1934-1996) | 
| Samuelson, Oskar (b. 1885) | Sand, George (1804-1876) | 
| Sandgren, John | Sanger, Margaret (1879-1966) | 
| Sanial, Lucien (1836-1927) | Sankey John (1866-1948) | 
| Sapronov, Timofei Vladimirovich (1887-1937) | Sarekat Islam [Islamic Association] | 
| Sartre, Jean-Paul (1905-1980) | Sasha | 
| Sastry, Vellala Srikantaya Seshagiri (1912– ca. 1982) | Saussure, Ferdinand de (1857-1913) | 
| Saville, John (1916-2009) | Savinkov, Boris (1879-1925) | 
| Savinkov, Boris Viktorovich (1879-1925) | Sazhen | 
| Scepticism & Dogmatism | Schäffe, Albert (1831-1903) | 
| Schüller, Richard (1901-1957) | Schaff, Adam (1913-2006) | 
| Schaffner, Erwin (1883-1942) | Schedrovitsky, Georgy (b. 1929) | 
| Scheflo, Olav (1883-1943) | Scheflo, Olav (1883-1943) | 
| Scheidemann, Philipp (1865-1939) | Scheidemann, Philipp (1865-1939) | 
| Scheidemanns | Schelling, Friedrich (1775-1854) | 
| Schelling, Friedrich Wilhelm Joseph  (1775-1854) | Scheu, Andreas 1844-1927 | 
| Schiffel, Jozef (1880-1959) | Schiller, Friedrich von  (1759-1805) | 
| Schippel, Max (1859-1947) | Schlüter, Hermann | 
| Schlick, Moritz (1882-1936) | Schmidt, Conrad (1863-1932) | 
| Schmidt, Robert (1864-1943) | Schober, Johann (1874-1932) | 
| Schober, Johannes  (1874-1932) | Schopenhauer, Arthur  (1788-1860) | 
| Schopenhauer, Arthur (1788-1860) | Schorlemmer, Carl  (1834-1892) | 
| Schramm, Karl | Schreiber, Hesekil (1899-1943) | 
| Schreiner, Albert (1892-1979) | Schreiner, Olive (1855-1920) | 
| Schulze, Ernst (1855-1932) | Schulze-Delitzsch, Franz Hermann (1808-83) | 
| Schumann, Georg (1886-1945) | Schwab, Alexander [Sachs] (1887-1943) | 
| Schwab, Charles M. (1862-1939) | Schwab, Michael (1853-1898) | 
| Schweitzer, Johann Baptiste von (1833-75) | Science | 
| Scientific Concept (Psychology) | Scoccimarro, Mauro (1895-1972) | 
| SDKP | SDKPiL | 
| SDKPiL | SDP | 
| Secchia, Pietro (1903-1973) | Sechenov, Ivan Mikhailovich (1829-1905) | 
| Second All-Russia Congress of Soviets of Peasants' Deputies | Second Congress | 
| Second Congress of the Russian Social-Democratic Labour Party | Second International | 
| Second International | Second International Conference in Zimmerwald, September 5th to 8th, 1915 | 
| Second International Congress in Amsterdam, August 14th to 20th 1904 | Second International Congress in Basel, November 24th to 25th 1912 | 
| Second International Congress in Copenhagen, 28th August to 3rd September 1910 | Second International Congress in Kienthal, April 24th to 30th, 1916 | 
| Second International Congress in London, July 21st to August 1st 1896 | Second International Congress in Paris, 23rd to 27th September 1900 | 
| Second International Congress in Stockholm, May to July, 1917 | Second International Congress in Stuttgart, 18th to 24th August 1907 | 
| Second International Congress of Brussels, 1891 | Second International Congress of Brussels, August 16th to 22nd 1891 | 
| Second International Congress of Zurich, August 6th to 13th 1893 | Secondary Contradictions (Psychology) | 
| Sectarianism and Opportunism | Section, Essential (Althusser) | 
| SED [Socialist Unity Party of Germany] | Sedan, Battle of (September, 1870) | 
| Sedgwick, Peter  (1934-1983) | Sedov, Leon (1906-1938) | 
| Sedov, Sergei  (1908-1937) | Seemann | 
| Seiden, Armin (1885-1931) | Seitz, Karl  (1869-1950) | 
| Self-consciousness | Self-identical | 
| Sellier, Henri (1883-1943) | Sellier, Louis (1885-1978) | 
| Selvarajatnan, Govindaswami (1924-1995) | Semashko, Nikolai (1874-1949) | 
| Sembat, Marcel (1862-1922) | Sembat, Marcel (1862-1922) | 
| Semblance | Semiology | 
| Semyonov, Grigorii Mikhailovich (1890-1946) | Sen, Indra Datta (? - 1996) | 
| Sen, Robin (1923-1995) | Senanayake, Reginald S. Vincent (1898– 1946) | 
| Separate Path theory | Serbian Socialist Party | 
| Serebryakov, Leonid Petrovich (1890-1937) | Serge, Victor (1890-1947) | 
| Serge, Victor (1890-1947) | Sergeyev, Artem F (d. 1921) | 
| Serrati, Giacinto Menotti (1874-1926) | Services | 
| Sethuraman | Seve, Lucien (1926-2020) | 
| Severing, Carl (1875-1952) | Sexism | 
| Sexton, James (1856-1938) | Shablin, Nikolai (1881-1925) | 
| Shachtman, Max (1904-1972) | Shaginyan, Marietta (1888-1982) | 
| Shapiro, L.G. (M. Shanin) (1887-1957) | Sharkey, Lance (1898-1967) | 
| Shastri, Onkarnath Verma (1908– c.2000) | Shastri, V. | 
| Shatskin, Lazar Abramovich (1902-1937) | Shaukat Ali, Maulana (1873-1938) | 
| Shaumyan, Stepan (1878-1918) | Shaw, George Bernard (1856-1950) | 
| Shingaryov, Andrei Ivanovich (1869-1918) | Shiroki (Broad) Socialists | 
| Shliapnikov, Alexander (1885-1937) | Shlyakhi (Paths) | 
| Shlyapnikov, Aleksandr Gavrilovich (1885-1937) | Shop Stewards [Britain] | 
| Shop stewards committees | Shoul, Bernice (1920-1977) | 
| Shukla, Chandravadan Pranjivan (1910– 2000) | Shumiatsky, Boris Zakharovich (1886-1938) | 
| Shumsky, Oleksander (1890-1946) | Siécle, Le | 
| Siberian Government | Siddaman, K. (1923 - present?) | 
| Siegfried, Jules (1837-1922) | Sievers, Max (1887-1944) | 
| Šik, Ota (1919-2004) | Silfs [Šilfs], Janis (1891-1921) | 
| Sinclair, Upton (1878-1968) | Singh, Bhagat (1907-1931) | 
| Sino-Soviet Split | Siriwardena, Coddipiliarachchi Don Reginald (1922– 2004) | 
| Sirola, Yrjö E. (1876-1936) | Sirola, Yrjö Elias (né Sirén) (1876-1936) | 
| Sirolle, Henri (1885-1962) | Sittampalam, V. (1911 –  1946) | 
| Skalàk, Josef (1874-1968) | Skinner, B. F. (1904-1990) | 
| Skobelev, Matvei Ivanovich (1885-1937) | Skoglund, Carl (1884-1960) | 
| Skorokhodova, Olga (1914-1982) | Slave Society | 
| Slavina, Liya (b. 1906) | Sliwinski, Artur (1877-1953) | 
| Slovo, Joe (1926-1995) | Slusarsji [Ślusarski] | 
| Small Bureau [Engeres Büro] | Smeral [Šmeral], Bohumir (1880-1941) | 
| Smeral, Bohumir (1880-1941) | Smidovich, Sofia Nikolaevna (1872-1934) | 
| Smilga, Ivar Tenisovich (1892-1938). | Smillie, Robert (1857-1940) | 
| Smillie, Robert (1857-1940) | Smirnov, Anatoli (1894-1980) | 
| Smirnov, Ivan (c. 1880-1936) | Smith, Adam (1723-1790) | 
| Smith, F.E., Earl of Birkenhead (1872-1930) | Smith, Gerald L. K. (1898-1976). | 
| Smuts, Jan Christian (1870-1950) | Smychka | 
| Smythe, Norah (1874-1963) | Sneevliet, Henk (1883-1942) | 
| Sneevliet, Henk (Maring) (1883-1942) | Snowden, Ethel (1881-1951) | 
| Snowden, Philip  (1864-1967) | Social Capital | 
| Social Chauvinism | Social Contract | 
| Social control and Integration | Social Democracy | 
| Social Democracy of the Kingdom of Poland | Social Democracy of the Kingdom of Poland and Lithuania | 
| Social Democratic Federation (SDF) | Social Democratic Labour Party of Bulgaria | 
| Social Democratic Labour Party of Germany | Social Democratic Party of Finland | 
| Social Democratic Party of Germany [SPD] | Social Democratic Party of Hungary | 
| Social Democratic Party of Serbia | Social Democratic Party of Slovakia | 
| Social Democratic Party of Sweden | Social Democratic Party of Switzerland | 
| Social Democratic Workers Party of Austria | Social fascism | 
| Social Imperialism | Social Movement | 
| Social Patriot | Social patriots | 
| Social situation of development (Psychology) | Social Wage | 
| Social-Demokrat | Socialisation | 
| Socialism | Socialism in one country | 
| Socialist Appeal (1941-1948) | Socialist Competition (or Emulation) | 
| Socialist Concentration | Socialist Democracy | 
| Socialist International (also: Second International; social-democracy) | Socialist Labor Party [SLP, US] | 
| Socialist Labor Party–SLP | Socialist Labour Association | 
| Socialist League | Socialist Ministerialism | 
| Socialist Party of America | Socialist Party of America | 
| Socialist Party of Great Britain | Socialist Party of India | 
| Socialist Party of Slovakia | Socialist Party of Uruguay | 
| Socialist Party, Australia | Socialist Party, French Section of the Workers International [SFIO] | 
| Socialist Party, Italy | Socialist Propaganda League | 
| Socialist Review (1934-1937) | Socialist Revolutionary Party | 
| Socialist Worker (1977-present) | Socialist Workers Party of Spain | 
| Socialist Workers Party, Chile | Socialist Workers Party, Finland | 
| Socialist World, The | Socialist-Revolutionary Party | 
| Society | Socrates (469-399 BCE) | 
| Soglia, Giuseppe (1871-1926) | Sojourner Truth (1969-1985) | 
| Sokolnikov, Grigorii Yakovlevich (1888-1939) | Sokolnikov, Grigory Y. (1888-1939) | 
| Sokolov, Alexander (b. 1911) | Sokolyansky, Ivan (1889-1960) | 
| Soldatskaya Pravda (Soldiers’ Truth) | Solidarity | 
| Solidarity | Solomon, T. M. | 
| Sombart, Werner (1863-1941) | Sombart, Werner (1863-1941) | 
| Sophists | Sorel, Georges  (1847-1922) | 
| Sorel, Georges (1847-1922) | Sorge, Friedrich Albert (1826-1906) | 
| Sorge, Richard (1895-1944) | Sosnovsky, Lev S.  (1886-1937) | 
| Sotsial-Demokrat (The Social-Democrat) | Soukup, František (1871-1940) | 
| Southern Worker, The (1930-1937) | Soutif, Edmond | 
| Souvarine, Boris  (1895-1984) | Souvarine, Boris (1895-1984) | 
| Soviet Government | Soviet Russia Pictorial (1923) | 
| Soviet Secret Police | Soviets | 
| Sovremenny Mir (The Contemporary World) | Sowjet [Soviet] | 
| Soysa, Bernard (1914– 1997) | Sozialistische Monatshefte (Socialist Monthly) | 
| SP | Spaak, Paul-Henri (1899-1972) | 
| Spanish Revolution (1931-1939) | Spargo, John (1876-1966) | 
| Spartacist (1964-present) | Spartacus | 
| Spartacus League (Spartacists) | Spartacus Rising (German Revolution 1918-19) | 
| Spartak (Spartacus) | SPD | 
| Special Theory of Relativity | Species Being | 
| Spector, Maurice (1898-1968) | Speculative Logic | 
| Spencer, Herbert (1820-1903) | Spender, Dale (1943-) | 
| Spengler, Oswald  (1880-1936) | Spies, August (1855-1887) | 
| Spinoza, Benidicto (1632-1677) | Spirit of the Times (Zeitgeist) | 
| Spiritual | Spontaneity (Althusser) | 
| Spontaneous concept (Psychology) | SRs | 
| SRs | St. Simon | 
| Stagflation | Stagism | 
| Stal’, Liudmila (1872-1939) | Stalin, Joseph (1879-1953) | 
| Stalinism | Stam, Jan Cornelis [Varkel] (1884-1943) | 
| Stampfer, Friedrich (1874-1957) | Standing Orders | 
| Stanić | Stasova, Elena (1873-1966) | 
| State | Steinhardt, Karl (1875-1963) | 
| Stepniak, Sergey Mikhailovich [Kravchinsky] (1851-95) | Stern, Victor (1885-1958) | 
| Stinnes, Hugo (1870-1924) | Stirner, Alfred | 
| Stirner, Max (1806-1856) | Stoddard, T. Lothrop (1883-1950) | 
| Stoecker, Walter (1891-1939) | Stoics | 
| Stokes, Rose Pastor (1879-1933) | Stoletov, Alexander Grigorievich (1839-1896) | 
| Stolypin's Agrarian Reform | Stolypin, Peter  (1862-1911) | 
| Strasser, Josef (1870-1935) | Stresemann, Gustav  (1878-1929) | 
| Striemer, Alfred (b. 1879) | Strong, Anna Louise (1885-1970) | 
| Structuralism | Structuralism (Althusser) | 
| Structure | Structure in Dominance (Althusser) | 
| Structure, Decentred (Althusser) | Struve, Peter (1870-1944) | 
| Struve, Pyotr (1870-1944) | Stuchka, Peter I. (1865-1932) | 
| Student Movement | Student Partisan (New York 1949-) | 
| Student Protest Movement | Student Socialist (1949-1951) | 
| Stukelj [Štukelj], Ciril (Marynko) (1903-50) | Sturc [Šturc], Vàclav (1858-1936) | 
| Sturm, Hertha (Edith Schumann) (1886-1945?) | Subasinghe, Mudiyanselage Tikiri Banda | 
| Subhi, Mustafa | Subhi, Mustafa Subhi (1883-1921) | 
| Subject | Subject (Psychology) | 
| Subject of Labour aka Object of Labour
 | Subjective | 
| Subjective and Objective (Psychology) | Subjective Idealism | 
| Subjective Logic | Subjectivism | 
| Subjectivity | Sublation | 
| Subsistence Standard | Substance | 
| Substance (Psychology) | Subsumption, Formal and Real | 
| Sudisman | Sukharno, Ahmed (1901-1970) | 
| Sukhomlin, Vasilii (1885-1963) | Sukhomlinov | 
| Sullivan | Sultanzade, Ahmed [Avetis Mikailian] (1889-1938) | 
| Sun Tzu | Sun Yat-sen (1866-1925) | 
| Sun Yat-sen (1866-1925) | Sundararajan, N. | 
| Supek, Rudi (1913-1993) | Supersession (Althusser) | 
| Superstructure / Structure (Althusser) | Suphi, Mustafa (1883-1921) | 
| Support (Althusser) | Surplus Value | 
| Suvorov, Alexander Vasilievich (1729-1800) | Suzuki, Bunji (1885-1946) | 
| Svehla [Švehla], Antonín (1873-1933) | Sverdlov, Yakov  Mikhaylovich (1885-1919) | 
| Swabeck, Arne (1890-1986) | Swedish Social Democrats | 
| Syllogism | Syn Otechestva (Son of the Fatherland) | 
| Synchrony / Diachrony (Althusser) | Syncretic concept (Psychology) | 
| Syndicalism | Synthesis | 
| System & Method | Szàntó, Béla (1881-1951) |