H1

H1, H-1, H01, H I and their variations may refer to:

• H1 (particle detector)
• H1, Histamine H1 receptor
• H1, Histone H1, a protein

• H1, British NVC community H1 heath zone
• H₁, hydrogen atom
• , one of the three laryngeals in the reconstructed Proto-Indo-European language
• , level 1 heading markup for HTML Web pages, see HTML element#heading
• H I region

 ATC code H01 Pituitary and hypothalamic hormones and analogues, a subgroup of the Anatomical Therapeutic Chemical Classification System statistical category of eyelid inflammations

• DSC-H1 camera
• Haplogroup H1, a grouping in genetics based on certain similarities

The laryngeal theory aims to produce greater regularity in the reconstruction of Proto-Indo-European phonology than in the reconstruction produced by the comparative method. Most notably, it seeks to extend the general occurrence of ablaut (apophony) to syllables that contain reconstructed vowel phonemes other than *e or *o.