Ha

Ha may refer to:

Agencies and organizations

Health authority, a former type of administrative organisation of the NHS in England and Wales
Hells Angels Motorcycle Club
Highways Agency (renamed Highways England, now National Highways), UK government body maintaining England's major roads
Homelessness Australia, peak body organisation for homeless people and services
Homosexuals Anonymous an ex-gay program for dealing with unwanted same-sex attractions
Hong Kong Housing Authority
Hospital Authority of Hong Kong

Hyperandrogenic anovulation, also called polycystic ovary syndrome
Health anxiety (HA) or hypochondriasis (hypochondria)
Hemagglutinin (influenza) (HA), an antigenic glycoprotein from Influenza viruses
Hemagglutination assay, a measurement of viruses or bacteria

ha (function prefix) (half), a prefix for some trigonometric functions in mathematics
Hallstatt culture, an archaeological culture
High availability, systems design and implementation with a view to maximising service
Hour angle, in astronomy, one of the coordinates of the equatorial coordinate system
H_a, or alternative hypothesis, in statistical testing
H-alpha (Hα), a deep-red visible spectral line of the hydrogen atom

Ha (Chinese surname) (哈), found in the Hundred Family Surnames
Ha (Korean surname) (하, 河 or 夏)
Hà, Vietnamese surname
Xia (surname) (夏), romanized as Ha in Cantonese, Korean and Vietnamese pronunciation

British Rail Class 71, a locomotive (classified type HA under the Southern Region's pre-TOPS scheme)
Hawaiian Airlines, former IATA designator HA
Highways Agency (now National Highways), UK government body maintaining England's major roads
Hungary (aircraft registration prefix HA)