Psychobilly (also known as punkabilly) is a rock music fusion genre that fuses elements of rockabilly and punk rock. It has been defined as "loud frantic rockabilly music", it has also been said that it "takes the traditional countrified rock style known as rockabilly, ramp[ing] up its speed to a sweaty pace, and combin[ing] it with punk rock and imagery lifted from horror films and late-night sci-fi schlock,... [creating a] gritty honky tonk punk rock."

Psychobilly is often characterized by lyrical references to science fiction, horror (leading to lyrical similarities to horror punk) and exploitation films, violence, lurid sexuality, and other topics generally considered taboo, though often presented in a comedic or tongue-in-cheek fashion. Psychobilly bands and lyrics usually take an apolitical stance, a reaction to the right- and left wing political attitudes which divided other British youth cultures. It is often played with an upright double bass, instead of the electric bass which is more common in modern rock music, and the hollowbody electric guitar, rather than the solid-bodied electric guitars that predominate in rock. Many psychobilly bands are trios of electric guitar, upright bass and drums, with one of the instrumentalists doubling as vocalist.

Psychobilly has its origins in New York City's 1970s punk underground, in which the Cramps are widely given credit for being progenitors of the genre and the first psychobilly band to gain a following. The music gained popularity in Europe in the early 1980s, with the UK band The Meteors, but remained underground in the United States until the late 1990s. The second wave of psychobilly began with the 1986 release of British band Demented Are Go's debut album In Sickness & In Health. The genre soon spread throughout Europe, inspiring a number of new acts such as Mad Sin (formed in Germany in 1987) and the Nekromantix (formed in Denmark in 1989), who released the album Curse of the Coffin in 1991. Since then the advent of several notable psychobilly bands, such as the U.S. band Tiger Army and the Australian band The Living End, has led to its mainstream popularity and attracted international attention to the genre.

The evolution of psychobilly as a genre is often described as having occurred in waves. The first wave occurred in New York City in the 1970s and reached Britain in the early 1980s, the second wave took place at the end of that decade and spread through the rest of Europe, and the third crested in the late 1990s with the genre finding international popularity.

The wildly theatrical shock rock aesthetic of Screamin' Jay Hawkins in the 1950s, and the outsider music of the Legendary Stardust Cowboy in the late 1960s have been cited as a precursor to what would become psychobilly. The members of the Meteors and the Cramps both cited the song "Love Me" (1960) by the Phantom as the first song in the genre.

The Cramps weren't thinking of this weird subgenre when we coined the term "psychobilly" in 1976 to describe what we were doing. To us all the '50s rockabillies were psycho to begin with; it just came with the turf as a given, like a crazed, sped-up hillbilly boogie version of country.

We hadn't meant playing everything superloud at superheavy hardcore punk tempos with a whole style and look, which is what "psychobilly" came to mean later in the '80s. We also used the term "rockabilly voodoo" on our early flyers.

In the mid- to late 1970s, as punk rock became popular, several rockabilly and garage rock bands appeared who would influence the development of psychobilly. The term "psychobilly" was first used in the lyrics to the country song "One Piece at a Time", written by Wayne Kemp for Johnny Cash, which was a Top 10 hit in the United States in 1976. The lyrics describe the construction of a "psychobilly Cadillac” using stolen auto parts.