SDN can stand for:
- S4C Digital Networks, a company that operates Multiplex A, one of the six groups of channels on digital terrestrial television in the United Kingdom
- SAP Developer Network, an online community for SAP developers
- Sandane Airport, Anda, an airport in the Gloppen municipality in Sogn og Fjordane, Norway, opened in 1975.
- Scottish Daily News, a left-of-centre daily newspaper published in Glasgow between May 5 and November 8, 1975
- Scottish Digital Network, a planned new public service broadcaster and online services provider in Scotland
- Sexually dimorphic nucleus, a cluster of cells in the brain that is believed to be related to sexual behavior in animals
- Sitecore Developer Network, an online community for Sitecore developers
- Software-defined networking, a software architecture allowing to define data flows in a network using software
- Specially Designated Nationals, individuals and organizations with whom United States citizens and permanent residents are prohibited from doing business
- Student Doctor Network, a nonprofit educational organization founded in 1999 for prehealth and health professional students in the US and Canada
- Subdeacon, a title used in various branches of Christianity
- Sudan, a country in northeastern Africa
- League of Nations, abbreviation in many official languages of the League; e.g., Société des Nations (French)