The series takes place in the 2020s and focuses on protagonists Kazuto "Kirito" Kirigaya and Asuna Yuuki as they play through various virtual reality MMORPG worlds, and later their involvement in the matters of a simulated civilization.

[3] The light novels began publication on ASCII Media Works' Dengeki Bunko imprint from April 10, 2009, with a spin-off series launching in October 2012.

An animated film titled Sword Art Online the Movie: Ordinal Scale, featuring an original story by Kawahara, premiered in Japan and Southeast Asia on February 18, 2017, and was released in the United States on March 9, 2017.

After the duo discover the identity of Kayaba's secret ID, who was playing as "Heathcliff", the leader of the guild Asuna joined in, they confront and destroy him, freeing themselves and the other players from the game.

Several months later, he is informed by Agil, another SAO survivor, that a figure similar to Asuna was spotted on "The World Tree" in another VRMMORPG cyberspace called Alfheim Online (ALO).

Assisted in-game by his cousin and adoptive sister Suguha "Leafa" Kirigaya and Yui, a navigation pixie (originally an AI from SAO), he quickly learns that the trapped players in ALO are part of a plan conceived by Sugou to perform illegal experiments on their minds.

The goal is to create the perfect mind-control for financial gain and to subjugate Asuna, whom he intends to marry in the real world, to assume control of her family's corporation.

Before leaving ALO to see Asuna, Kayaba, who has uploaded his mind to the Internet using an experimental, destructively high-powered version of NerveGear at the cost of his life, entrusts Kirito with The Seed – a package program designed to create virtual worlds.

Kazuto eventually reunites with Asuna in the real world after thwarting an attack from Sugou and The Seed is released onto the Internet, reviving Aincrad as other VRMMORPGs begin to thrive.

During his time in Underworld, Kirito befriends Eugeo, a carver in a small village of Rulid, and helps him on a journey to save Alice Zuberg, his friend who was taken by a group of highly skilled warriors known as the Integrity Knights for accidentally breaking a rule of the Axiom Church, the leaders of the Human Empire.

He and Eugeo soon find themselves uncovering the secrets of the Axiom Church, led by a woman only known as "The Administrator", and the true purpose of Underworld itself, while unbeknownst to them, a war against the opposing Dark Territory is brewing on the horizon.

One month later, Kirito, Asuna, and the others have their accounts forcibly migrated to Unital Ring, a new VRMMORPG which incorporates locations from all the other environments they previously visited, and investigate the cause while meeting some familiar faces.

[14] An original 100-page prequel novel to Sword Art Online the Movie: Ordinal Scale written by Kawahara, titled Hopeful Chant, was released to people who watched the film in Japan during March 4–10, 2017.

[18] The novels are also published in China, Taiwan, South Korea, Thailand and Vietnam,[19] with future plans for publications in France,[20] Germany, Italy, Austria, Switzerland and others.

[25][26] A comedy four-panel manga, titled Sword Art Online (そーどあーと☆おんらいん。) and illustrated by Jūsei Minami, began serialization in the September 2010 issue of Dengeki Bunko Magazine.

[27] A third manga, titled Sword Art Online: Fairy Dance (ソードアート・オンライン フェアリィ・ダンス) and illustrated by Hazuki Tsubasa, began serialization in the May 2012 issue of Dengeki Bunko Magazine.

[17] A spin-off manga starring Lisbeth, Silica, and Leafa, titled Sword Art Online: Girls Ops (ソードアート・オンライン ガールズ・オプス) and illustrated by Neko Nekobyō, began serialization in the July 2013 issue of Dengeki Bunko Magazine.

A seventh manga, titled Sword Art Online: Calibur and illustrated by Shii Kiya, was serialized in Dengeki G's Comic between the September 2014 and July 2015 issues.

[37] An eighth manga, titled Sword Art Online: Mother's Rosario and also by Tsubasa, is based on the seventh volume of the novel series and began serialization in the July 2014 issue of Dengeki Bunko Magazine.

[41] An anime adaptation of Sword Art Online was announced at Dengeki Bunko Autumn Festival 2011, along with Reki Kawahara's other light novel series, Accel World.

[70] However, the season ended at episode 24 on March 30, 2019 (completing the fourteenth volume of the novel, Alicization Uniting), and continued on October 12, 2019, with a second part titled War of Underworld.

[71][72] The second half of the War of Underworld series was originally scheduled to premiere in April 2020,[73] but due to the effects of the COVID-19 pandemic in Japan,[74] it was rescheduled to air from July 11 to September 19, 2020.

The song was composed by Yuki Kajiura and performed by Reona, Asca, and Eir Aoi, who were in charge of previous opening and ending themes for the series.

[110] A social network game called Sword Art Online: End World was released for Japanese feature phones and smartphones on February 28, 2013[111][112] with more than 1 million registered users.

[150] Featuring content from the anime series, Ordinal Scale, and some original shorts written for event characters, players are allowed to play solo and progress through the story, or join up with others online to farm special items, equipment, and materials.

Bandai Namco released the Sword Art Online: Integral Factor free-to-play MMORPG for Android and iOS in December 2017, created in conjunction with prolific mobile MMO developer Asobimo [ja].

[154] Bandai Namco Entertainment released the Sword Art Online VR: Lovely Honey Days mobile game for iOS and Android devices in Japan in October 2018.

[166] Laeta Kalogridis has been attached to write a script for the pilot, and will also serve as executive producer for the series alongside Skydance CEO David Ellison, Dana Goldberg, and Marcy Ross.

[180] Richard Eisenbeis of Kotaku hails Sword Art Online as the smartest series in recent years, praising its deep insight on the psychological aspects of virtual reality on the human psyche, its sociological views on creating a realistic economy and society in a massively multiplayer online game setting, and the writing staff's ability to juggle a wide variety of genres within the series.

[183] Theron Martin of the same website criticized the story as struggling "to achieve and maintain the level of gravitas that life-or-death danger should have", while calling it unwilling to commit to Kirito's "lone wolf" image.