Atrium may refer to:
- Atrium (architecture), a large open space within a building usually with a glass roof
- Atrium (alveoli), microscopic air sacs in lungs
- Atrium (heart), an anatomical structure of the heart
- Atrium of the ventricular system of the brain
- Atrium (Cardiff), a University of Glamorgan (Wales) building in Cardiff
- Atrium, the genital structure next to the genital aperture in the reproductive system of gastropods
- Atrium, an alternative rock band.