Throughout their 35-plus-year career, Yes have always treated the concert stage as both a playground and a laboratory, reshaping and revivifying their music just about every night. This three-disc box, which showcases the differing personalities of the group's multiple lineups over the years, brings together nearly four hours of live performances, capturing the earliest flowerings of their classical-rock hybrid as well as the sharpened pop-rock hooks of their late-'80s period. In addition to soaring versions of favorites like "Yours Is No Disgrace" and "I've Seen All Good People," the collection's first disc spotlights the developing band's uncanny knack for putting their imprint on a wide array of cover tunes. The intricate interplay of their take on Paul Simon's "America" is well known, but just as impressive is their languid, loving rendition of "It's Love" (culled, rather surprisingly, from the catalog of blue-eyed soul pioneers the Rascals). Disc 2 finds the band at the summit of their improvisational skills, particularly on pieces like "Siberian Khatru," on which guitarist Steve Howe and keyboardist Rick Wakeman trade off solos with abandon, and "Sound Chaser," transformed into a wild ride by vocalist Jon Anderson. Diehards will no doubt be particularly hypnotized by a 25-minute, six-part segment dubbed "The Big Medley," which clearly wowed the Los Angeles crowd, judging by the cheers greeting every turn in these grooves. The Word Is Live's final disc is a bit more schizophrenic, as it covers a full decade (and a number of internal changes). At the onset -- as borne out by the epic "Awaken," led by Wakeman's medieval organ -- Yes were still in full-on prog mode, but as the disc develops, a more song-oriented focus emerges, via tunes like "Shoot High Aim Low" and "Owner of a Lonely Heart." For fans of Yes -- or anyone with a more cerebral take on rock -- Live is a four-letter word well worth uttering.