S6 or S-6 may refer to:

Routes

• S6 (Berlin), a S-Bahn line
• S6 (Milan suburban railway network)
• S6 (Munich), a S-Bahn line in Munich
• S6 (Rhine-Main S-Bahn)
• S6 (Rhine-Ruhr S-Bahn), line
• S6 (St. Gallen S-Bahn)
• S6 (ZVV), a S-Bahn line in the cantons of Zürich and Aargau in Switzerland
• County Route S6 (California)
• Expressway S6 (Poland)
• Essex, a county of England
• S6 postcode, covering areas of north western Sheffield
• a Hanover S-Bahn, line
• a Rhein-Ruhr S-Bahn, line
• a Rhine-Main S-Bahn, line
• a Stuttgart S-Bahn, line
• a Stadtbahn Karlsruhe, line
• Tongmi line

Science

• Ribosomal protein s6
• S6: Keep under ... (inert gas to be specified by the manufacturer), a safety phrase in chemistry
• hexasulfur, a cyclic sulfur allotrope
• the symmetric group of degree six

Technology

• Samsung Galaxy S6, a smartphone produced by Samsung
• Samsung Galaxy Tab S6, an Android tablet
• S6 NBC Respirator, the protective gas mask issued to the British armed forces from 1966 up until the introduction of the current-issue S10 in 1986
• S6 truss, a part of the International Space Station

Vehicles

• Audi S6, a car
• ALCO S-6, and American diesel switching (shunting) locomotive
• Prussian S 6, a 1906 steam locomotives class
• Rans S-6 Coyote II, a light aircraft
• Supermarine S.6, and Supermarine S.6B, two 1929 and 1931 racing seaplanes
• USS S-6 (SS-111), a 1919 S-class submarine of the United States Navy
• HMS Cachalot (S06), a 1957 British Porpoise-class submarine

Other uses

• S6 (military), a communications officer within military units
• Star Air (Denmark), IATA airline designator
• S6 (classification), a paralympic swimming classification