Jam bands, technically, have been around since the dawn of music, ever since the first homosapien was joined by another in the pursuit of a collective sound. Country porch communities, folk hootenannies and late-night jazz clubs thrived on the jam aspects of the musicians’ performances.

But the connotation of jam bands — that of a group of long-haired rock groups expanding their minds and the time boundaries of their songs — began in the late ’60s, when artists such as Grateful Dead began exploring new directions in their music.

It didn’t end, however, when hippie idealism faded, as reflected in the list below of the Top 20 Jam Band Albums, which was selected by the UCR staff. The records include British electric blues pioneers, German experimentalists, patched-together supergroups and, yes, Grateful Dead, to whom much of the music released since the ’70s leads.

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The best of these albums, which include a mix of studio and live recordings, share a common love of finding new ways to sustain excitement in the music. In many cases, the versions of songs included on the albums were nothing more than launching pads for the live setting, where they would take on new shapes and textures nightly. (Witness “Whipping Post,” a perfectly good blues imitation included on the Allman Brothers Band‘s self-titled debut album that quickly became a 23-minute live showcase.)

The definitive jam band LPs often capture that live experience. Even when they don’t, there’s a thrilling sense of working without a net, as if everything could suddenly shift to another solo or chord progression at any moment. That’s what is celebrated below.