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
- s6 (software), a software suite providing process supervision in Unix-like systems. See Why "s6".
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 (1929), and Supermarine S.6B (1931), British 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
- Staff (military), a communications officer within military units
- Star Air (Denmark), IATA airline designator
- S6 (classification), a paralympic swimming classification