Although subtitled Ultimate '66 garage classics!, not all of the recordings on the album were originally released in 1966.

The first CD collects tracks from the first 10 CDs in the Pebbles series plus Ear-Piercing Punk, while the second CD are "insanely rare bonus tracks" that are previously un-reissued in any form (except for 2 that were previously included on a rare 1982 compilation album).

As mentioned in the introductory liner notes, the recordings on the first CD serve as "a sort of 'greatest hits' for seasoned listeners" as well as an introduction to the Pebbles series, with the inclusion of well-known garage and psychedelic classics such "Green Fuz", "I Never Loved Her", "She's Not Just Anybody", and "Doin' Me In."

The final cut, "Go Go, Girl," by the Hombres, was released as the B-Side of the single "Let It All Hang Out" in 1967, is attributed to an "unknown artist", and its lyrics' feature a male narrator expressing his frustration about having to "stand in line" to see his girlfriend become a "hip-swingin', fringe-slingin' Watusi go go girl" in the presence of other men.

Unlike most of the AIP compilations, the liner notes are spare and convey little information.