.Hack (pronounced dot hack)is a story set around 2010. The main focus is on a game called The World. The project was created simultaneously on many different media formats, each telling its own, complete story, but all adding up to make the complete story.

On December 24th 2005, a virus called Pluto's Kiss took down the entire internet for over an hour. There was complete chaos with so much technology dependant on the internet at that point, many secure systems such as the US defence computers started to malfunction, the stock exchange crashed, hospital computers went down, traffic systems and air control towers didn't work. In the aftermath all forms of network entertainment were restricted.

Soon afterwards, the ALTIMIT OS was developed to ensure a secure network that would not be vulnerable to almost all common forms of cyber crime. It quickly became the most popular OS, by October 2007 almost 100% of computers were running ALTIMIT. On December 24th, all restrictions on the use of the internet were lifted and the first online game for years is released, The World.

.Hack's story is split up into the following:

.hack//AI BUSTER (Novel): A prequel to the main story, talking about the creator of The World, Harold Hewick, what happened at the start and talking about the wandering AIs.

.hack//SIGN (26 part anime TV series): A few years after The World's release, a player called Tsukasa is trapped inside the game by the AI Morgana, who is trying to stop the AI Aura from awakening.

.hack//ZERO (Novel): Discusses the events between SIGN and INFECTION.

.hack//INFECTION (PS2 game) (aka Infection Expansion): Part 1 of 4. This RPG series follows the story of the player Kite who is caught up in the events when Aura give him a bracelet that allows him use of Data Drain, he becomes the only person who has the power to deal with the virus that is corrupting The World.

.hack//MUTATION (PS2 game) (aka Malignant Mutation): Part 2 of 4.
.hack//OUTBREAK (PS2 game) (aka Erosion Pollution): Part 3 of 4.
.hack//QUARANTINE (PS2 game) (aka Absolute Encirclement): Part 4 of 4.

.hack//LIMINALITY (anime OVA): A four part series that follows the events in the real world at the same time as games. One episode of the OVA comes with each volume of the game.

.hack//UDEDEN (manga and 13 part anime TV series) (aka "Tasogare no Udewa Densetsu", ".hack//DUSK", "Legend of the Bracelet of the Twilight" and "Legend of the twilight"): Follows the story of the players Shugo and Rena, who were awarded the costumes of the legendary dot hackers (Kite and Blackrose). It takes place a few years after the events of the games when there is another spate of characters being taken into comas by The World.

Note about the titles: The title DUSK was made up by some fansubbers looking for a shortened title, obviously they didn't know much about .hack because twilight (twilight and dusk both being translations of "udewa") is an important event referred to in ALL of .hack (they even use the English word), so firstly they should have used "twilight" rather than "dusk" and it isn't even distinctive of the series. "UDEDEN" is the shortened title, "Legend of the Bracelet of the Twilight" or "Legend of twilight's bracelet" are the translations of the full Japanese title (Bracelet of the Twilight fits better into how Twilight is refered to in the series). "Legend of the Twilight" is the official English title.

.hack//ENEMY Is the collectable card game.