H3

H3, H03 or H-3 may refer to:

Entertainment

 * Happy Hustle High, a manga series by Rie Takada, originally titled "H3 School!"
 * H3 (film), a 2001 film about the 1981 Irish hunger strike
 * h3h3Productions, styled "[h3]", a satirical YouTube channel

Science

 * Triatomic hydrogen (H3), an unstable molecule
 * Trihydrogen cation (H3+), one of the most abundant ions in the universe
 * Tritium (Hydrogen-3, or H-3), an isotope of hydrogen
 * ATC code H03 Thyroid therapy, a subgroup of the Anatomical Therapeutic Chemical Classification System
 * British NVC community H3, a heath community of the British National Vegetation Classification system
 * Histamine H3 receptor, a human gene
 * Histone H3, a component of DNA higher structure in eukaryotic cells
 * *h3, one of the three laryngeals in the reconstructed Proto-Indo-European language
 * Hekla 3 eruption, a huge volcanic eruption around 1000 BC

Computing

 * , the level-3 HTML heading markup element
 * HTTP/3, the third revision of a protocol for the World Wide Web
 * Socket H3, the common name of the LGA 1150 CPU socket

Air and space

 * H3 (rocket), an expendable launch system under development by Japan Aerospace Exploration Agency
 * Harbour Air Seaplanes (IATA code), a Canadian charter airline
 * H-3 Air Base, former Iraqi Air Force base in western Iraq
 * H-3 Sea King, a United States Navy helicopter
 * Standard H-3, an improved version of the 1916 Standard H-2 aircraft

Automobiles

 * Brilliance H3, a Chinese compact sedan
 * Haval H3, a Chinese compact SUV
 * Huansu H3, a Chinese compact MPV
 * Hummer H3, an American mid-size SUV

Ships

 * USS H-3 (SS-30), a 1914 United States Navy H-class submarine
 * HMS Grenville (H03), a 1935 British Royal Navy destroyer
 * HMS H3, a 1915 British Royal Navy H-class submarine
 * H3, a yacht build by Oceanco

Rail

 * H3 series of METRORail tramways in Houston
 * GNR Class H3, a class of British steam locomotives

Roads

 * H3 Monks Way, a road part of the Milton Keynes grid road system, United Kingdom
 * Interstate H-3, a highway in Hawaii

Other uses

 * H3 (classification), a para-cycling classification
 * H3, an 18th-century marine chronometer by John Harrison
 * H3, a type of automotive halogen lamp
 * H3 (pyrotechnics), a pyrotechnic composition
 * H3 Hardy Collaboration Architecture, a firm started by Hugh Hardy
 * H3 Pharmaceutical Chemistry, an advanced subject for GCE A-level students in Singapore
 * DSC-H3, a 2008 Sony Cyber-shot camera
 * Hash House Harriers, an international group of non-competitive running, social and drinking clubs
 * H3 (Kuwait), an archaeological site
 * H3 Entertainment, a subsidiary of the film industry company The H Collective