Progressive rock is an ambitious, eclectic, and often grandiose style of rock music which arose in the late 1960s principally in England, reaching the peak of its popularity in the early 1970s, but continuing as a musical form to this day. Progressive rock was largely a European movement, and drew most of its influences from clasical music and jazz fusion, in contrast to American rock, which was influenced by rhythm & blues and country, although there are notable exceptions in the New World such as Kansas and Rush — considered by many to be the finest examples of the form. Over the years various sub-genres of progressive rock have emerged, such as symphonic rock, art rock and progressive metal.
Progressive rock artists sought to move away from the limitations of radio formatted rock and pop, and "progress" rock to the point that it could achieve the sophistication of jazz or classical music. It is admired by its fans for its complexity, requiring a high level of musical virtuosity to perform. Critics have often derided the genre as pompous and self-indulgent. This is because, unlike such stylistically consistent genres as country or hip-hop, progressive rock is difficult to define in a single conclusive way. Outspoken King Crimson leader Robert Fripp has voiced his disdain for the term. The major acts that defined the genre in the 1970s (Yes, Genesis, Emerson Lake and Palmer, Rush and King Crimson) do not sound alike. There is also debate on whether bands such as The Beatles, Phish, and Radiohead belong to the genre.