British rock describes a wide variety of forms of music made in the United Kingdom. Since around 1964, with the "British Invasion" of the United States spearheaded by the Beatles, British rock music has had a considerable impact on the development of American music and rock music across the world. Initial attempts to emulate American rock and roll took place in Britain in the mid-1950s, but the terms "rock music" and "rock" usually refer to the music derived from the blues rock and other genres that emerged during the 1960s. The term is often used in combination with other terms to describe a variety of hybrids or subgenres, and is often contrasted with pop music, with which it shares many structures and instrumentation. Rock music has tended to be more orientated toward the albums market, putting an emphasis on innovation, virtuosity, performance and song writing by the performers. Although much too diverse to be a genre in itself, British rock has produced many of the most significant groups and performers in rock music internationally, and has initiated or significantly developed many of the most influential subgenres, including beat music, progressive rock, art rock, hard rock, heavy metal, punk, post-punk, New Romantic, and indie rock. Early British rock and roll In the 1950s, Britain was well placed to receive American rock and roll music and culture. It shared a common language, had been exposed to American culture through the stationing of troops in the country, and shared many social developments, including the emergence of distinct youth sub-cultures, which in Britain included the Teddy Boys. Trad jazz became popular, and many of its musicians were influenced by related American styles, including boogie-woogie and the blues. The skiffle craze, led by Lonnie Donegan, utilised mostly amateurish versions mainly of American folk songs and encouraged many of the subsequent generation of rock and roll, folk, R&B and beat musicians to start performing. At the same time British audiences were beginning to encounter American rock and roll, initially through films including Blackboard Jungle (1955) and Rock Around the Clock (1955). Both films contained the Bill Haley & His Comets hit "Rock Around the Clock", which first entered the British charts in early 1955 - four months before it reached the US pop charts - topped the British charts later that year and again in 1956, and helped identify rock and roll with teenage delinquency. American