STX may be:
- An abbreviation for South Texas
- STX (sports manufacturer), a sports manufacturer based in Baltimore, Maryland.
- A common abbreviation for St Croix, U.S. Virgin Islands.
- An abbreviation for St Cross College, Oxford.
- A secure private telephone network used by London Stock Exchange affiliated firms and professionals.
- Henry E. Rohlsen Airport (IATA: STX), an airport on St. Croix, U.S. Virgin Islands.
- Studentereksamen, an examination used in Denmark for the secondary school called gymnasium.
- STX Corporation, a Korea-based holding company.
- STX Pan Ocean, a Korea-based shipping company.
- Streaming Transformations for XML, an XML transformation language.
- Start of Text, a control code in the C0 control code set.
- Seagate Technology, a manufacturer of hard disk drives for PC and many entertainment devices, based on its stock symbol STX.
- Saxitoxin, a neurotoxin found in marine dinoflagellates.
- Syntaxin
- An acronym for Star Trek Nemesis (Star Trek X)
- Case STX Steiger
- Shiga toxin
- Filename extension of the PASTI raw disk image format for the Atari ST
- Structured Text, a plaintext markup language.