Progressive rock

Progressive rock, often shortened to prog rock or prog, is a form of rock music characterized by lengthy and complicated forms (often based on classical or jazz, and frequently consisting of multiple contrasting sections), the use of instruments not typically found in rock, and complicated harmonies and rhythms. Other defining features include the "concept album" (such as Dark Side of the Moon or The Wall), fantasy-based lyrics, and artistic album covers.

Progressive rock arose during the late 1960s and carried on through the 1970s before a decline corresponding to the rise of punk. King Crimson, Yes, Emerson, Lake, & Palmer, and Genesis are considered the four "classic" exponents of this genre, although bands as diverse as Pink Floyd, Jethro Tull, and Rush have been given this label.

The genre has been criticized for some of its excesses and pretensions, which led to its downfall in the late 1970s (although bands like Pink Floyd and Rush continued to maintain a large following). In the 1980s, many artists in this genre commercialized their sound to incorporate the New Wave movement and other more mainstream rock fads, while in the 1990s a new wave of "progressive metal" bands arose who combined the sound of traditional prog bands with metal bands such as Black Sabbath and Metallica.