Progressive metal (often shortened to prog metal) is a broad fusion music genre melding heavy metal and progressive rock, combining the loud aggression and amplified distorted guitar-driven sound of the former with the more experimental, cerebral or quasi-classical compositions of the latter.

The music typically showcases the extreme technical proficiency of the performers and usually uses unorthodox harmonies as well as complex rhythms with frequent meter changes and intense syncopation. The polyrhythmic aspects are especially emphasized in the djent subgenre.

Although the genre emerged towards the late-1980s, it was not until the 1990s that progressive metal achieved widespread success. Dream Theater, Watchtower, Queensrÿche, Tool, Symphony X, Shadow Gallery, King's X, Fates Warning, and Mastodon are a few examples of progressive metal bands who achieved commercial success.

Progressive metal, as a distinct musical style, was primarily advanced by members of the American heavy metal scene of the mid-1980s, particularly Queensrÿche, Savatage, Fates Warning, Watchtower and then later on, Dream Theater and Symphony X. It has since developed in a non-linear fashion, with countless groups demonstrating innovations in personal ways.

The origins of the genre date back to the very beginning of heavy metal/hard rock and progressive rock when some bands began to merge the two different approaches. 1960s pioneers King Crimson maintained their musical innovation while incorporating a harder approach, using dissonance and experimental tones, yet still maintaining a relationship to the power chords of hard rock, with the main example being "21st Century Schizoid Man". Canadian trio Rush is widely recognized as bridging the gap between hard rock, English progressive rock, and pure heavy metal. Initially influenced by Led Zeppelin, they evolved to combine established progressive rock technique with blues-based power chords. Records such as 2112 (1976) showcased technical expertise and complex compositional skill while still utilizing a more direct and heavier approach than the well-established English progressive rock sound.

1984 brought full-length debut albums from American bands Queensrÿche from Washington state, and Fates Warning from Connecticut. Both expanded their music to include more progressive elements (The Warning, 1984; The Spectre Within, 1985) – some through sound experimentation and compositional refinement, others through extremely complex structures and atypical riffs – up to the two seminal works in 1986: Rage for Order and Awaken the Guardian. In the following years the two bands, while following different paths – more basic and simple the first, more articulate and complex the latter — explore and expand the technical refinement and sonic finesse of their music, continuing to lay the foundations of the genre with important works such as Operation: Mindcrime (1988) by Queensrÿche, and Perfect Symmetry (1989) by Fates Warning.

Progressive metal also found a home in the growing U.S. thrash metal movement, and many bands of the genre released albums that drew elements and influences of progressive music, including the "Big Four" of thrash metal — Metallica (Ride the Lightning, 1984; Master of Puppets, 1986; ...And Justice for All, 1988), Slayer (Hell Awaits, 1985), Anthrax (Persistence of Time, 1990), and Megadeth (Rust in Peace, 1990). Bands that took a technical and progressive approach similar to the "Big Four" were Toxik (World Circus, 1987; Think This, 1989), Overkill (The Years of Decay, 1989), Dark Angel (Leave Scars, 1989; Time Does Not Heal, 1991), and Bay Area thrash metal bands Forbidden (Twisted into Form, 1990), Heathen (Victims of Deception, 1991), and, on some of their late 1980s and 1990s output, Testament. One of the most notable thrash metal bands outside of the U.S. is Canada's Voivod, with their complex and experimental style, full of psychedelic dissonances (Dimension Hatröss, 1988; Nothingface, 1989). "Math-metal" pioneers Watchtower, from Texas, took the concept of time-changes to a new level, combining thrash metal, syncopation and prog in their albums Energetic Disassembly (1985) and Control and Resistance (1989), giving rise to an extremely technical approach based on the rhythmic deconstruction typical in jazz fusion. This same direction in prog metal would be later integrated into death metal by bands such as Atheist (Unquestionable Presence, 1991), which would become known as technical death metal or progressive death metal. Bands which also explored fusion-inspired prog metal include most notably Death and Cynic.

The major US bands that contribute to further delineating and developing the genre are Psychotic Waltz and Dream Theater. The former, with an approach halfway in between Watchtower and Fates Warning, produced A Social Grace (1990), melding their signature sound with the psychedelic Into the Everflow (1992), while the latter explored the legacy of the bands that preceded them while advancing their personal style with When Dream and Day Unite (1989). Both albums focused on keyboards and band members' instrumental skills. As for Dream Theater, their efforts resulted in two fundamental albums, which helped institutionalize classic progressive metal — Images and Words (1992) and Awake (1994). King's X, who emerged from a Christian rock background, incorporated their sound with influences of hard rock, metal, progressive rock, funk, soul and bands from The Beatles to U2 on their early albums — particularly their first three albums, Out of the Silent Planet (1988), Gretchen Goes to Nebraska (1989) and Faith Hope Love (1990) — before leaning more towards an alternative and grunge-inspired hard rock sound on their later output, including the highly-successful Dogman (1994). Other hard rock bands from this era that experimented with influences of progressive music into their sound include Europe, The Cult, Winger, Living Colour, Mr. Big, and Extreme.