en Hydra

Hydra generally refers to:

Lernaean Hydra, a many-headed serpent in Greek mythology
Hydra (genus), a genus of simple freshwater animals belonging to the phylum Cnidaria

Hydra or The Hydra may also refer to:

Astronomy

Hydra (chess), a chess computer
Hydra (digital repository), an open-source digital repository software product later renamed Samvera
Hydra (operating system), an early, discontinued, capability-based, object-oriented microkernel
Hydra (software), a parallelized network login cracker built in various operating systems
Hydra (specification), a specification for REST APIs
Hydra 100, a multi-GPU hardware solution
HYDRA Game Development Kit, a development system by André LaMothe
Razer Hydra, a game controller
NEC HYDRAstor, a storage system

Hydra (comics), a fictional organization in the Marvel Universe
- Hydra (Marvel Cinematic Universe), an organisation in the Marvel Cinematic Universe based on the comics counterpart
Hydra (Dungeons & Dragons), a fictional monster in D&D
Hydra (Transformers), a character in Transformers
The Hydra, a fictional organization in The Phantom
Hydra, a character in UFO Ultramaiden Valkyrie
The Hydra, a fictional deity created by Henry Kuttner
- Mother Hydra, the co-ruler of the Deep One race in the Cthulhu Mythos
The Hydra, a fictional fighter jet in Grand Theft Auto: San Andreas and Grand Theft Auto Online
The Hydra, a fictional machine in Kirby Air Ride
Hydra, a boss enemy in the video game Prototype 2

Hydra (ship), a hydrogen ship
Greek ironclad Hydra, a French-built ironclad warship launched in 1889
Greek destroyer Hydra, a Dardo-class destroyer launched in 1932
Greek frigate Hydra, a MEKO 200-type frigate launched in 1992, lead ship of the Hydra class frigate
HMS Hydra (1797), a 38-gun fifth rate
HMS Hydra (1838), a wooden steam paddle sloop
- Hydra-class sloop, a class of British steam sloops
HMS Hydra (1871), a Cyclops-class turret ship
HMS Hydra (1912), an Acheron-class destroyer
HMS Hydra J275), an Algerine-class minesweeper launched in 1942
HMS Hydra (A144), an oceanographic survey vessel launched in 1965
Hydra-class minelayer, a class of Dutch 1910s minelayers
HNLMS Hydra (A854), a Duch Navy diving support vessel

The Hydra, a literary magazine
Hydra (association), a German self-help and advocacy group for prostitutes
Hydra (video game), an arcade and Atari Lynx video game
Hydra game, a concept in mathematical logic
Hydra Market, a Russian language dark web marketplace that facilitated trafficking of illegal drugs as well as financial services
Hydra the Revenge, a roller coaster at Dorney Park in Pennsylvania, US
Hydra 70, an air-to-ground rocket
Hydra Technologies, an unmanned aerial vehicle firm
Hydra Trophy, a trophy of the roller derby WFTDA Championships
Hydra, a wireless station during World War II at Camp X
Operation Hydra (Yugoslavia)
Operation Hydra (1943)