HOS may stand for:
- Hammer of the Scots (board game), a board game
- Head of State
- Hearts of Space, a radio program
- Hellenic Ornithological Society
- Holt-Oram syndrome
- Home Ownership Scheme by the Hong Kong Housing Authority
- Hoosier Southern Railroad by reporting mark
- Hornbeck Offshore Services by stock ticker symbol
- Hours of service, laws limiting commercial truck driver working hours
- Hyper Operating System, a fictional OS designed to run Labors, specifically construction labors, in Patlabor
- Croatian Defence Forces, abbreviated "HOS" in Croatian, the military arm of the Croatian Party of Rights (1991–1993)
- Croatian Armed Forces (NDH), abbreviated "HOS" in Croatian, the military of the Independent State of Croat
- Health Outcomes Survey