ICOS was an American biotechnology company.
ICOS may also refer to:
- ICOS (gene), a gene which encodes the protein CD278
- Integrated Carbon Observation System, a research infrastructure
- Integrated cavity output spectroscopy, a type of laser absorption spectrometry
- International Council of Onomastic Sciences, an academic organization
- The International Council on Security and Development, an international think tank
- Irish Co-operative Organisation Society, a business association