Nu metal (sometimes stylized as nü-metal, with a metal umlaut) is a subgenre of alternative metal that combines elements of heavy metal music with elements of other music genres such as hip hop, funk, industrial, and grunge. Nu metal rarely features guitar solos or other displays of musical technique and emphasizes rhythm with instrumentation that is heavily syncopated. Nu metal guitarists often use seven-string guitars that are down-tuned to produce a heavier sound. Vocal styles are often rhythmic and influenced by hip hop, and include singing, rapping, screaming and sometimes growling. DJs are occasionally featured to provide instrumentation such as sampling, turntable scratching and electronic background music. Nu metal is one of the key genres of the new wave of American heavy metal.

In the late 1980s and early 1990s, bands like Pantera, Helmet, and Faith No More were influential in the development of nu-metal with their groove metal and alternative metal styles. Korn is often credited as pioneering the subgenre in the mid-1990s with their self-titled debut album. Nu metal became popular in the late 1990s, with bands and artists such as Korn, Limp Bizkit, and Slipknot all releasing albums that sold millions of copies. Its popularity continued through the early 2000s, with bands such as Papa Roach, Staind, and P.O.D. all selling multi-platinum albums. The popularity of nu metal came to a peak in 2001 with Linkin Park's diamond-selling album Hybrid Theory. By the mid-2000s, however, the oversaturation of bands combined with the underperformance of several high-profile releases led to the subgenre's decline, leading to the rise of metalcore and many nu-metal bands disbanding or abandoning their established sound in favor of other genres.

The 2010s brought a nu-metal revival; many bands that combined it with other genres (for example, metalcore and deathcore) emerged, and some nu-metal bands from the 1990s and early 2000s returned to the nu-metal sound. Bands such as Of Mice & Men, Emmure, Issues, My Ticket Home, and Bring Me the Horizon combined nu metal with metalcore or deathcore. Artists like Grimes, Poppy, and Rina Sawayama integrated nu-metal sounds into electronic pop music in the late 2010s and early 2020s, and interest in nu metal rose in the early 2020s.

Nu metal is a subgenre of alternative metal. Sometimes stylized as nü-metal, the genre has also been dubbed aggro-metal or simply aggro. MTV states that the early nu metal group Korn "arrived in 1993 into the burgeoning alternative metal scene, which would morph into nü-metal the way college rock became alternative rock." Stereogum similarly said that nu metal was a "weird outgrowth of the Lollapalooza-era alt-metal scene". Nu metal merges elements of heavy metal music with elements of other music genres such as hip hop, grunge, funk, and alternative rock according to Blabbermouth.net. Nu metal bands use many elements of heavy metal genres such as rap metal, groove metal, and funk metal. Some nu metal bands, such as Static-X and Dope, made nu metal music with elements of industrial metal. In contrast with other heavy metal subgenres, nu metal tends to use the same structure of verses, choruses, and bridges as those in pop music.

Then a funny thing happened: myopic anti-rap sentiment within more conservative heavy metal quarters saw a slew of new bands already busy blurring these genre lines (Faith No More, Infectious Grooves, etc.) repositioned as “funk metal”; but this did nothing to slow down the increasing cross-pollination, as some bands added record-scratching DJs to their arsenal. Finally, a generation of groove metal bands led by Texas’ Pantera brought a new level (pun intended) of rhythmic elements into heavy metal, and most of the ingredients were finally in place for bands like Korn, Deftones, Slipknot and Limp Bizkit to kickstart and coalesce the Nu-Metal craze.

Instrumentation in nu metal is heavily syncopated and is based mostly on guitar riffs, although these riffs are prominent, guitar solos are not integrated heavily within the genre. These riffs often being inspired by groove metal. Mid-song bridges and the general lack of guitar solos contrasts it with other genres of heavy metal. Kory Grow of Revolver wrote, "... [i]n its efforts to tune down and simplify riffs, nu-metal effectively drove a stake through the heart of the guitar solo". Another contrast with other heavy metal genres is nu metal's emphasis on rhythm, rather than on complexity or mood. The wah pedal is occasionally featured in nu metal music.

Nu metal bassists and drummers are often influenced by funk and hip hop, respectively, adding to nu metal's rhythmic nature. Blast beats and double bass drumming, which are both common in heavy metal subgenres such as black metal, thrash metal and death metal, are uncommon in nu metal, with drummers such as Slipknot's Joey Jordison and Mudvayne's Matt McDonough being notable exceptions. Nu metal's similarities with many heavy metal subgenres include its use of common time, distorted guitars, and power chords and note structures primarily revolving around Dorian, Aeolian or Phrygian modes. While loud and heavily distorted electric guitars are a core feature of all metal genres, nu metal guitarists took the sounds of "violence and destruction" to new levels with their overdriven guitar tone, which music journalists Kitts and Tolinski compared to the "...sound [of] a Mack truck being crushed by a collapsing skyscraper."

Some nu metal bands use seven-string guitars that are generally down-tuned, rather than traditional six-string guitars. Likewise, some bass guitarists use five-string and six-string instruments. Bass guitar-playing in nu metal often features an emphasis on funk elements. In nu metal music, DJs are sometimes featured to provide instrumentation such as sampling, turntable scratching and electronic backgrounds. Nu metal tends to have hip hop grooves and rhythms.