ISA
- In Shaa' Allah, means "God Willing" in Arabic
- Intelligent speed adaptation
- Intelligence Support Activity, a special operations unit of the U.S. Army
- Infectious salmon anemia, a viral disease of salmon
- ISA (Days of our Lives), International Security Alliance, fictional spy agency on the NBC soap opera Days of our Lives
- Independent Safeguarding Authority, a body created in England, Wales and Northern Ireland to help prevent those who pose a known risk from working with children and vulnerable adults
- International Society of Arboriculture, a non-profit botanical organization
- International Sociological Association, a non-profit organization in the fields of sociology and the social sciences
- ITER Staff Association - a union of employees of the ITER Organization
- International Standard Atmosphere, a definition of pressure, temperature, humidity and so forth, under the SI convention
- Interplanetary Strategic Alliance, an alliance in the Killzone series of video games.
- International Symbol of Access, an image of a stylized person in a wheelchair against a blue background, meant to designate handicap accessibility at a glance
- Interstellar Alliance, an alliance in Babylon 5 to fight the Shadows
- Irish Sailing Association, the governing body for sailing in Ireland
- ISA (company), Intelligent Sensing Anywhere, a Portuguese company specialized in telemetry and M2M (Machine to Machine) communications
- International Surfing Association is the world governing authority for the sport of surfing
- International Society of Automation (formerly known as Instrument Society of America)
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