Alternative metal (also known as alt-metal and grunge metal) is a genre of heavy metal music that combines heavy metal with influences from alternative rock and other genres not normally associated with metal. Alternative metal bands are often characterized by heavily downtuned, mid-paced guitar riffs, a mixture of accessible melodic vocals and harsh vocals and sometimes sounds that are unconventional within other heavy metal styles. The term has been in use since the 1980s, although it came into prominence in the 1990s.

Other genres considered part of the alternative metal movement included rap metal and funk metal, both of which influenced another prominent subgenre, nu metal. Nu metal expands the alternative metal sound, combining its vocal stylings and downtuned riffs with elements of other genres, such as hip hop, funk, thrash metal, hardcore punk and industrial metal.

Alternative metal began in the 1980s with bands like Faith No More, Living Colour, Soundgarden, and Jane's Addiction. The genre achieved success in the 1990s with the popularity of bands like Helmet, Tool, and Alice in Chains. In the late 1990s and early 2000s, nu metal achieved mainstream popularity with the mainstream success of bands like Korn, Limp Bizkit, P.O.D., Papa Roach, Disturbed, System of a Down, Linkin Park, Slipknot, Deftones and Staind. After the mid-2000s, nu metal's popularity began to decline, with many nu metal bands moving on to other genres.

One of the main characteristics of alternative metal and its subgenres are heavily downtuned, mid-paced "chug"-like guitar riffs. However, funk metal bands often use a more conventional riffing style influenced by 1980s thrash metal. Alternative metal features clean and melodic vocals, influenced by those of alternative rock, in contrast to other heavy metal subgenres. Later bands frequently incorporated vocal styles that alternated between clean singing, growls and screaming. Examples include alternative metal bands associated with the nu metal movement, such as Korn and Deftones, who have been described as having "bipolar vocals".

Jonathan Gold of the Los Angeles Times wrote in 1990 "Just as rock has an alternative, [left] wing-bands like the Replacements and Dinosaur Jr.-so does metal. Alternative metal is alternative music that rocks. And alternative metal these days can reach 10 times the audience of other alternative rock. Jane's Addiction plays an intense brand of '70s-influenced arty metal; so does Soundgarden. In fact, the arty meanderings of Sabbath and Zeppelin themselves would be considered alternative metal." Houston Press has described the genre as being a "compromise for people for whom Nirvana was not heavy enough but Metallica was too heavy."

The first wave of alternative metal bands emerged from many backgrounds, including hardcore punk (Bad Brains, Rollins Band, Life of Agony, Corrosion of Conformity), noise rock (Helmet, the Jesus Lizard, Today Is the Day), Seattle's grunge scene (Alice in Chains, Soundgarden), stoner rock (Clutch, Kyuss), sludge metal (Fudge Tunnel, Melvins), gothic metal (Type O Negative), groove metal (Pantera, White Zombie) and industrial (Godflesh, Nine Inch Nails, Ministry). These bands never formed a distinct movement or scene; rather they were bound by their incorporation of traditional metal influences and openness to experimentation. Jane's Addiction borrowed from art rock and progressive rock, Quicksand blended post-hardcore and Living Colour injected funk into their sound, for example, while Primus were influenced by progressive rock, thrash metal and funk and Faith No More mixed progressive rock, R&B, funk and hip hop. Fudge Tunnel's style of alternative metal included influences from both sludge metal and noise rock.

The origins of the genre can be traced back to funk rock music of the early to mid-1980s, when alternative bands like Fishbone, Faith No More and the Red Hot Chili Peppers started mixing heavy metal with funk, creating the alternative metal subgenre funk metal. Other early bands in the genre also came from hardcore punk backgrounds. Bands such as Faith No More, Jane's Addiction and Soundgarden are recognized as some of the earliest alternative metal acts, with all three of these bands emerging around the same time, and setting the template for the genre by mixing heavy metal music with a variety of different genres in the mid to late 1980s. During the 1980s, alternative metal appealed mainly to alternative rock fans, since virtually all 1980s alt-metal bands had their roots in the American independent rock scene. Living Colour was another alternative metal band that combined the genre with funk metal.

The emergence of grunge as a popular style of rock music in the early 1990s helped make alternative metal more acceptable to a mainstream audience, with alternative metal soon becoming the most popular metal style of the 1990s. Several bands associated with the genre denied their status as metal bands. Helmet drummer John Stanier said "We fell into the whole metal thing by accident, we always hated it when people mentioned metal in conjunction with us." Helmet's Meantime (1992) album became one of the most influential heavy metal albums of the 1990s. Saby Reyes-Kulkarni of Pitchfork Media stated "bands like Faith No More, Soundgarden, Primus, Helmet, the Rollins Band, and dozens more were initially marketed as quasi-metal acts. This was only possible in a climate where record labels, journalists, and college radio DJs understood that the metal audience could embrace new, albeit arty variations on the form."