By 1967, the most creative British bands had exhausted their fascination with American blues and early rock and roll, and even main-stream British Invaders such as the Beatles and the Rolling Stones were pushing the boundaries of "rock." Artists opened themselves to a huge variety of influences?from Indian classical music to European avantgarde electronics and widespread use of psychedelic drugs fueled their desire for evermore exotic sounds, while imbuing the proceedings with mystical airs. it was out of this psycho-acoustic love fest that progressive rock emerged.

What exactly is progressive rock? That depends on whom you ask. Enthusiasts laud the music's ambitious compositional scope, virtuosic instrumental excursions, literary lyrics, and overall sonic majesty, while detractors decry its overarching pretentiousness, interminable solos, self absorbed lyrics, and overblown arrangements. in fact, dozens of bands from the '60s and '70s are routinely lumped together under the progressive rock ban-ner, and, whatever one makes of them, their styles often differ dramatically. Add to that the hundreds of "neo-progressive" and "progressive metal" bands that have followed in their wake, and a comprehen-sive defınition of the music remains as elusive as an acid vision.

One thing, however, is certain: Many of the artists hoped to legitimize rock as a serious art form by elevating it to a level of sophistication equal to that of jazz and classical music, and to that end they appropriated instrumentation and compositional elements from both. But other influences entered the mix as well, including American and British Isles folk, psychedelia, opera, and electronic. Bands specifically cited as progressive rock precursors (and sometimes considered to be progressive bands them-selves) include England's Pink Floyd, Traffıc, and Deep Purple; and America's Spirit, Magic Band, and Mothers of Invention; as well as the early British "Canterbury Scene" bands, such as the Wilde Flowers, Soft Machine, Caravan, and Gong; and Miles Davis' "electric period" bands.

Though progressive rockers appeared worldwide, particularly in Europe, for the purposes of this brief overview we'll consider the music as a British phenomenon occurring between 1968 and 1976, taking a few of the most influential artists as examples.