ISN is an initialism that can stand for:
- International Relations and Security Network, a free public service that provides products and resources to encourage the exchange of information among international relations and security professionals worldwide.
- International Suppliers Network, a vendor tracking system.
- International Society for Neurochemistry
- Interstellar Network News, a news network in the fictional Babylon 5 universe.
- Idioma de Signos Nicaragüense meaning Nicaraguan Sign Language in the Spanish language.
- Sloulin Field International Airport, Williston, North Dakota, USA (IATA airport code)
- Internment Serial Number, a number which captives of the United States Armed Services apprehended during its war on terror are assigned.
- Initial Sequence Number, a number exchanged in TCP segments during computer network communication between a client and a server. Central in a SYN flood defense known as SYN cookies.
- Intel Software Network
- InfoSec News
- Institut de Santé Naturelle (ISN or ISNFR) Fleury Rodet
- Superphénix
- ITAD Subscriber Numbers, a method of providing inter-domain numeric Session Initiation Protocol addressing, allowing SIP URIs to be dialled numerically.