Progressive rock, or in its abbreviated form Prog Rock, is a sub-genre of rock music, which emerges in the United Kingdom and Germany towards the end of the 1960 decade, developing gradually in Europe, then worldwide, during the next decade. Pulling its origin from the psychedelic rock, this current has the particularity of conferring rock a greater artistic credibility. It is characterized by the remoteness of the format of popular music in favor of musical and instrumental techniques more associated with jazz and classic music. Progressive rock is characterized by its rhythmic, harmonic, and instrumental experiments. Added to this is a certain freedom in the choice of instruments: keyboards and synthesizers, in particular, occupy an important place within the progressive formations. The addition of several instruments judged foreign to rock music - the flute, the saxophone, the violin, the vibraphone, or even the harmonium, in particular - is also common. The peak of the popular rock...