Key is a Japanese visual novel video game development studio and brand under the publisher VisualArt's. The video games developed by Key are initially published by VisualArt's and released for Microsoft Windows personal computers; consumer ports are published by Interchannel and Prototype. Key released their debut title, Kanon, in 1999, followed by their second title, Air, in 2000. Both Kanon and Air were initially released as adult games, but Key released their third game, Clannad, in 2004 with a rating of approval for all ages. Key's fourth game, Planetarian: The Reverie of a Little Planet, was also released in 2004 with a rating for all ages, and is described as a "kinetic novel" by the development team because of its completely linear storyline.
Key's fifth game, Tomoyo After: It's a Wonderful Life, was released in 2005 as an adult game and spin-off from Clannad; it expanded on the scenario of the heroine Tomoyo Sakagami. Key released their sixth visual novel, Little Busters!, in 2007 with a rating for all ages. Key's seventh title, Little Busters! Ecstasy, was an expanded, adult version of Little Busters! released in 2008. Key's eighth game, Kud Wafter, was released in 2010 as an adult game and spin-off from Little Busters! Ecstasy; it expanded on the scenario of the heroine Kudryavka Noumi. Key released their ninth game Rewrite in 2011 with a rating for all ages. Key released a fan disc of Rewrite titled Rewrite Harvest festa! in 2012. The first volume in the episodic Angel Beats! visual novel was released in 2015. Key released the kinetic novel Harmonia in 2016. Key has announced the visual novel Summer Pockets.
As of September 2016, 42 versions of Key's 12 released visual novels have been published by VisualArt's. Of the 42, 11 were released with an adult rating, and the remaining 31 had a rating for all ages. VisualArt's has ceased manufacturing 21 versions of Key's 12 games. Key released a box set called "Key 10th Memorial Box" in July 2009 containing six of Key's visual novels with a rating for all ages. The availability of Key 10th Memorial Box was restricted to ordering online. Key released "memorial editions" of their first five games in April and May 2010 with ratings for all ages.