From the perspective of 15 subsequent platinum albums and 20 top-10 hits, it's hard to imagine that Chicago began their career as a bona fide prog-fusion act, an early FM radio favorite whose jazz-tinged, album-length suites found them a hip cult following even as they confounded label execs. Ironically, when the pioneering horn band (a contemporary of Blood, Sweat & Tears and inspiration for one-hit wonders like Lighthouse, Ides of March, and Ten Wheel Drive) relented and allowed their music to be edited down to single length, their success was explosive. Most of the "single edits" on disc 1 of this 39-track anthology provide ample evidence of that de facto formula: a catchy riff ("25 or 6 to 4," "Saturday in the Park," "Color My World") develops into a hook-filled, pop-savvy production rife with the band's trademark horn perfection. One could argue that that sensibility--and a midcareer tilt toward producer David Foster, songwriter Diane Warren, and the MOR ballads that became some of their biggest successes--degenerated into formula. Indeed, there's much on the second disc to support that notion. This set spans it all, showcasing newly refocused edits of some their biggest early hits and lesser-known tracks like their lively '95 cross-cultural collaboration with the Gipsy Kings on a cover of Louis Prima's swing classic "Sing, Sing, Sing."