The Guitar Hero series (sometimes referred to as the Hero series) is a series of music video games first published in 2005 by RedOctane and Harmonix Music Systems, and distributed by Activision, in which players use a guitar-shaped peripheral to simulate the playing of lead, bass guitar and rhythm guitar across numerous rock music songs. Players match notes that scroll on-screen to colored fret buttons on the controller, strumming the controller in time to the music in order to score points, and keep the virtual audience excited. The games attempt to mimic many features of playing a real guitar, including the use of fast-fingering hammer-ons and pull-offs and the use of the whammy bar to alter the pitch of notes. Most games support single player modes, typically a Career mode to play through all the songs in the game, and both competitive and cooperative multiplayer modes. With the introduction of Guitar Hero World Tour in 2008, the game includes support for a four-player band including vocals and drums. The series initially used mostly cover version of songs created by WaveGroup Sound, but most recent titles feature soundtracks that are fully master recordings, and in some cases, special re-recordings, of the songs. Later titles in the series feature support for downloadable content in the form of new songs.

RedOctane, then a company primarily in the manufacture of unique game controllers, was inspired in 2005 to create Guitar Hero based on their experience with creating hardware for Konami's GuitarFreaks arcade game, and enlisted the help of Harmonix Music Systems, who had previously developed several music video games, for development duties. The first game in the series was made on a budget of $1 million. The series became extremely successful, leading to, in 2007, the acquisition of RedOctane by Activision, while Harmonix was acquired by MTV Games and went on to create the Rock Band series of music games in the same vein as Guitar Hero. Activision brought Neversoft (primarily known for their Tony Hawk series of skateboarding games) on board for future development duties. Additional companies, such as Vicarious Visions, Budcat Creations, Machineworks Northwest, and Aspyr Media have assisted in the adoption of the games for other systems.

The game currently has seven major releases and four expansions on gaming consoles, and with spinoffs for Windows and Macintosh systems, mobile phones, the Nintendo DS, and an arcade game, with several more titles announced for future release. The Guitar Hero franchise has become a cultural phenomenon and learning and development tool for medical purposes, and has impacted both the video game and the modern music industry. The first game in the series was considered by several journalists to be one of the most influential video games of the first decade of the 21st century. The series has sold more than 25 million units worldwide, earning US$2 billion at retail, claimed by Activision to be the 3rd largest game franchise after the Mario and Madden NFL franchises; the third main title of the series, Guitar Hero III: Legends of Rock is also claimed by Activision to be the first single video game title to exceed $1 billion in sales.