Homeworld: Cataclysm is a 2000 real-time strategy video game developed by Barking Dog Studios and published by Sierra Studios for Windows. It is the second entry in the Homeworld series and was originally developed as an expansion for Relic Entertainment's Homeworld, but was ultimately released as a stand-alone sequel. Set fifteen years after the events of the first game, Cataclysm follows the Kuun-Lan, a Kushaan mining starship that attempts to counter "the Beast", a destructive nanobot virus, while combatting the imperialist remnants of the Taiidan Empire, who seek revenge on the Kushaan and control of Hiigara.

The game was released on September 1, 2000 in North America and September 29, 2000 in Europe to positive critical reception, and was nominated for numerous strategy game of the year awards. In June 2017, the game was rereleased on GOG.com as Homeworld: Emergence, as the name "Cataclysm" was trademarked by Blizzard Entertainment for its third expansion of World of Warcraft. Talks of a remake by Gearbox Software were reportedly conducted around the mid-2010s, but as of 2025 little news has surfaced since.

Though it uses the same engine and similar gameplay as its predecessor, several changes were made, such the ability to toggle time compression between normal speed and eight times faster; ship upgrades (improving armor and adding new abilities); Command Ships and Carriers receiving the ability to add external modules for ship research and fleet support; Command Ships having attack capabilities; fuel being removed from gameplay; and the sensor display could be used to issue attack orders to units. The player's Command Ship is now capable of dealing powerful attacks. The game also introduced new 3D features such as moving parts and transforming ships.

Notable unit changes include the Processor, Cataclysm's adaptation of the Resource Controller, which has medium-strength weapons to defend itself, automated repair beams to heal nearby ships and four pads to dock with Workers harvesting resources. The game's resource collectors perform the same functions that they did in the original Homeworld, however, when upgraded they can be used to capture enemy vessels, harvest crystals and repair friendly vessels; functions that were carried out by separate, single-function ships in the first game.

In general, the main difference is the scale of fleets. Where Homeworld was biased towards large fleets (as the player's main ship was a full-fledged mothership and the opposition was an empire of galactic scale), Cataclysm down-scales the fleets (as the player's main ship is a simple mining vessel and the adversaries are all limited in resources).

Fifteen years after the events of Homeworld, the Kushaan people have established themselves on Hiigara and are now governed by a council formed from the leaders of their clans, or "kiith." The Taiidan Empire has collapsed, though Imperialist remnants and their allies, the Turanic Raiders, still threaten the Hiigarans and the new Taiidani Republic.

The story begins with Kuun-Lan, a mining vessel belonging to the minor kiith Somtaaw, joining ships from several other kiith to repel an Imperialist attack on Hiigara, but being ignored when the other kiith are thanked for their help. While helping another fighter defend itself against a Turanic Raider assault, the Kuun-Lan finds a derelict beacon pod that does not resemble any known technology. Their kiith-Sa (clan leader) insists that the find be kept secret due to the political advantage it might provide and sends the science ship Clee-San to help study it. However, as research begins, a strange virus begins to overtake the ship, and the Kuun-Lan is forced to jettison the affected section to avoid being completely overrun. When the Clee-San attempts to investigate further, it is infected by the virus, which soon spreads to a nearby group of Turanic Raider ships. The infected ships attack and attempt to assimilate the Kuun-Lan, forcing it to flee.

Kuun-Lan discovers that the pod they picked up was contaminated with techno-organic nanobots that can subvert both machinery and organic tissue, which they code-name "the Beast." As the Beast continues to spread and infect more ships, it grows more intelligent and strategic in its tactics, speeding its growth further and threatening to overwhelm Hiigaran and Taiidani Republic forces trying to hold it at bay. Kuun-Lan traces the source of the Beast to the Naggarok, an alien vessel from another galaxy whose crew disabled their own ship in order to contain the Beast after encountering it in hyperspace. However, the ship fired off an infected distress beacon which was eventually discovered by the Kuun-Lan, unleashing the Beast on the galaxy.