H0 (H followed by zero) or H00 may refer to:
- H0 scale, used in rail transport modelling
- Higgs boson, in physics, symbol H0
- Hammett acidity function, in chemistry, H0
- Hubble constant, in cosmology, H0
- Null hypothesis, in statistics, often denoted H0
- HMS Comet (H00), a British and later Canadian warship
- Stye, a bacterial infection of the eyelid, ICD-10 code H00