Key was founded on July 21, 1998 by Jun Maeda, Shinji Orito, and Itaru Hinoue, after they parted ways with their previous employer Tactics to work at Visual Art’s. The Key brand officially belongs to Jun Maeda. The company released their debut title Kanon on June 4, 1999. Although being an adult visual novel, Key kept scenes with intercourse to a minimum to focus on the story. Key continued this with their second title Air, which was also an adult visual novel that places focus on the story rather than sex. Both Kanon and Air were later released with the adult content removed. Clannad was Key’s third release and was the first of Key’s releases that features no adult content at all. Clannad was followed by Planetarian ~Chiisana Hoshi no Yume~ and then Tomoyo After: It’s a Wonderful Life, which is an adult spin off of Clannad. Key then released Little Busters! which had an all ages version and a subsequent 18+ version. Key's most recent visual novel is 2018's Summer Pockets.
Key has met with great success in the Japanese market and have had a strong influence on the visual novel genre, however most outside of Japan became familiar with Key from the many anime adaptations of their works, especially Clannad. Although fan translations of Key's works have existed since the early 2000s, Key's first official English-language release would not occur until 2011's iOS port of Planetarian. Following the success of Planetarian's later Steam port, all three Clannad games received an English translation in 2016, followed by Little Busters! the subsequent year.
- A number of Key’s releases have received anime adaptations, most notably Kanon, Air, Clannad, Little Busters, and Planetarian.
- The music from Key’s games are released under the label Key Sounds Label.
- In the late 2000s, Key ran an internet radio service called Key Net Radio. Through the service, Key would discuss company happenings and information about games they were actively developing. The service's final episode was released on August 30, 2010.