Released in December 1965 — and capping a year that had been defined by groundbreaking singles such as Bob Dylan's "Like a Rolling Stone" and the Rolling Stones' "(I Can't Get No) Satisfaction" — Rubber Soul finds the Beatles rising to meet the challenge their peers had set. Characteristically, they achieved a new musical sophistication and a greater thematic depth without sacrificing a whit of pop appeal. Producer George Martin described Rubber Soul as "the first album to present a new, growing Beatles to the world," and so it was.

The band's development expressed itself in a variety of overlapping ways. On the U.K. version (the only one available on CD), "Drive My Car" presents a comic character study of a sort that had not previously been in the Beatles' repertoire. More profoundly, however, Dylan's influence suffuses the album, accounting for the tart emotional tone of "Norwegian Wood," "I'm Looking Through You," "You Won't See Me" and "If I Needed Someone." (Dylan would return the compliment the following year, when he offered his own version of "Norwegian Wood" — titled "4th Time Around" — on Blonde on Blonde, and consequently made Lennon "Paranoid.") Lennon's "Nowhere Man," which he later acknowledged as a depressed self-portrait, and the beautifully reminiscent "In My Life" both reflect the more serious and personal style of songwriting that Dylan had suddenly made possible.

Musically speaking, George Harrison's sitar on "Norwegian Wood" — the first time the instrument was used in a pop song — and Paul McCartney's fuzz bass on "Think for Yourself" document the band's increasing awareness that the studio could be more than a pit stop between tours. From this point on, a fascination with the sonic possibilities of recording would inspire the Beatles' greatest work.

Harrison called Rubber Soul "the best one we made," because "we were suddenly hearing sounds that we weren't able to hear before." And as for why the band's hearing had grown so acute, well, that was another aspect of the times. "There was a lot of experimentation on Rubber Soul," said Ringo Starr, "influenced, I think, by the substances."