S42 may refer to:
Aviation Blériot-SPAD S.42, a French biplane trainer aircraft Sikorsky S-42, an American flying boat Springer Municipal Airport, in Colfax County, New Mexico, United States
Rail and transit S42 (Berlin), a railway line of the Berlin S-Bahn, Germany S42 (Long Island bus) S42 (New York City bus), serving Staten Island S42 (ZVV), a railway line of the Zurich S-Bahn, Switzerland
Science S42 (selective androgen receptor modulator) S-42 (geodetic datum), used in Eastern Europe S42: During fumigation/spraying wear suitable respiratory equipment (appropriate wording to be specified by the manufacturer), a safety phrase Sulfur-42, an isotope of sulfur
Submarines , of the Argentine Navy , of the Royal Navy , of the Indian Navy , a submarine of the United States Navy
Other uses IBM NetVista S42, a personal computer Siemens S42, a mobile phone Zulu language S42, a postcode district in Chesterfield, England