Ultimate Classic Rock Top 50...

"We were only talking the other day about the possibility of rock music — in the next 10 years — really developing into a higher art form," Jon Anderson told Sounds in 1971, the year Yes released two prog-rock classics, The Yes Album and Fragile. "Rock musicians will make music that will last a hell of a lot longer in the future."

He was right on two levels. As bands like Yes, Genesis and King Crimson flourished in the late '60s and early '70s, adding classical structure and jazz chops to their amplified rock, their compositions began to swell in the literal sense: Epic pieces like "Supper's Ready" and "Close to the Edge" were long enough to warrant bathroom breaks.

But that period remains the genre's golden age for a reason: Before go-to prog moves bred tropes, before imitators ran amok and watered everything down, these artists experimented without a rule book.

That messiness and wildness makes prog a tricky genre to pin down. Symphonic prog, heavy prog, prog-pop, avant-prog, the Canterbury Scene, RIO, Zeuhl, progressive electronic, folk-prog, jazz-fusion— at a certain point, it's almost easier to say what doesn't qualify. And even as the genre's more traditional sounds have fallen out of fashion, others have emerged from the indie and metal worlds, giving the mutating movement new life.

All of this to say: In some ways, it's easy to pick the Top 50 Progressive Rock Albums. Many of the entries toward the top of our list are unimpeachable. But also: It's almost impossible. There's so much, in such varied styles, that you automatically exclude hundreds of essential titles by imposing an arbitrary numerical limit. Even if you disagree with some of these choices — and let's face it, you're gonna — we hope you'll approach our list as a platform for discovery. And isn't "discovery" the point of prog anyway?