Guitar Hero II is a music video game developed by Harmonix Music Systems and published by RedOctane. It is the second installment in the Guitar Hero series and is the sequel to Guitar Hero. It was first released for the PlayStation 2 in November 2006 and then for the Xbox 360 in April 2007, with additional content not originally in the PlayStation 2 version.

Like in the original Guitar Hero, the player uses a guitar-shaped peripheral to simulate the playing of rock music as notes scroll towards the player. Most of the gameplay from the original game remains intact, with new modes and note combinations being the major additions. The game features more than 40 popular licensed songs, many of them cover versions recorded for the game, spanning five decades (from the 1960s to the 2000s). The PlayStation 2 version of Guitar Hero II can be purchased individually or in a bundle that packages the game with a cherry red Gibson SG guitar controller. The Xbox 360 version of the game is offered in a bundle that packages the game with a white Gibson X-Plorer guitar controller. Both of these controllers are wired, but RedOctane also sells a wireless controller for the PlayStation 2.

Since its release, Guitar Hero II has been met with both critical and commercial success, helping the Guitar Hero series become a cultural phenomenon. As of December 1, 2007, the game has sold 3.1 million copies. It has spawned the "expansion" title Guitar Hero Encore: Rocks the 80s for the PlayStation 2. A full-fledged sequel, Guitar Hero III: Legends of Rock, has been released by Neversoft, the makers of the popular Tony Hawk series. Harmonix, the previous developers of the Guitar Hero series, went on to produce Rock Band, a similar rhythm game that features guitar, bass, drum and microphone gameplay.

The surprise success of Guitar Hero readily led to the development of a sequel for the game. :According to developer John Tam, the team felt they "hit the sweet spot" of genres and decades within the set list and wanted to maintain that for the sequel. The costs of obtaining licensing rights for music from "big bands" such as AC/DC, Led Zeppelin, Van Halen, and Metallica, in addition to the lack of understanding of how the music would be used prevented these groups from being used in Guitar Hero. However, Tam notes that with the success of Guitar Hero, "They understand that we're not going to embarrass their music, we're going to actually pay homage to their music and get it to the point where people are going to fall in love with their music and understand their music in a totally different way than they've ever experienced it before." They also had requests by artists to include master tracks within the game.

In addition to working more directly with artists, RedOctane and Activision worked with various musical instrument and equipment companies to provide in-game product placement. Such vendors include BOSS Effectors, DW Drums, Eden Bass Amplication, EMG, Epiphone, Ernie Ball Strings, Gibson Guitar Corporation, Guitar Center, Hofner, Kramer, Krank, Line 6, Mesa Boogie, MusicMan Basses, Orange Amplifiers, Randall Amplifiers, Roland, Vans and the Vans Warped Tour, VHT, and Zildjian.

Guitar Hero II was originally announced for the PlayStation 2 on April 17, 2006. A demo version of the PlayStation 2 version of Guitar Hero II was released with issue #110 of Official PlayStation Magazine on October 5, 2006. Features of the demo included four playable songs on four difficulty levels for single player and co-op modes. Demo releases do not feature the ability to flip the notes for left-handed players. Demo versions feature the songs "Shout at the Devil", "You Really Got Me", "Strutter" and "YYZ". The demo featured slightly different note charts than the final release for some of the songs.[citation needed] The retail game was released for the PlayStation 2 on November 7, 2006 in North America, November 15, 2006 in Australia, and November 30, 2006 in the United Kingdom and Europe. It was released as both a stand-alone game and as a bundle containing the game and a cherry Gibson SG guitar controller.

When Activision purchased RedOctane in 2006, the company expressed strong interest in bringing the Guitar Hero series to "every significant new format" in order to take advantage of the next generation of consoles. The Xbox 360 version was announced on September 27, 2006 at Microsoft's X06. Dusty Welch of RedOctane stated that the Xbox 360 "provides an incredible platform for facilitating downloadable content" due to the integrated hard drive on the console. The Xbox 360 version of the game included 10 exclusive songs and additional content available for purchase through the Xbox Live Marketplace.

The Xbox 360 version was released on April 3, 2007 in North America and Australia, and then on April 6, 2007 in Europe, only as a bundle containing the game and a wired Gibson X-Plorer guitar controller.). It was released as a stand-alone game for the Xbox 360 in the UK on January 25, 2008.

Gameplay is based on the successful formula created for the first Guitar Hero game; the player may use the guitar peripheral to play scrolling notes by holding the corresponding fret button on the guitar neck and simultaneously pressing the strum bar. Alternatively, one can play with the DualShock 2 or Xbox 360 controller by using four shoulder buttons and a face button, mapped to specific fret keys.

Several changes have been made to the gameplay mechanics for Guitar Hero II: hammer-on and pull-off functionality has been improved, and three note chords have been introduced, scored as triple points if played correctly. There are additional statistics available for a song upon completion, and the scores achieved in either Quick Play or Career mode are saved to the same in-game high-score list. The handedness of the guitar can now be toggled from the Pause menu when playing a song (previously, this was only available from the game's main menu). For the Xbox 360 version, scores can also be compared with other players through Xbox Live via the Leaderboard feature, and there are 50 Achievements that can be earned in the game.