The album that many have hailed as both The Beatles' and pop music's masterpiece was unleashed onto the public on this day in 1967.
If you want to do some quick reading on it, here's Pitchfork's review of the digitally remastered Pepper, and here's Slate's (truly insightful) commemoration of the 40th anniversary of the album's release.
Excerpt from the former:
Lyrically, it's an atypical way to usher in the Summer of Love, but musically, the record is wildly inventive, built on double-tracking, tape effects, and studio technology. The dream-like haze of "Lucy in the Sky With Diamonds", the fairground, sawdust feel of "Mr. Kite", and the cavalcade of sound effects at the end of "Good Morning Good Morning" were the most demonstrative sounds on the record, but otherwise benign passages were also steeped in innovation, whether recording from the inside of a brass instrument or plugging instruments directly into the sound board instead of capturing them through mics.
Almost everything done on Sgt. Pepper's turned out to be new and forward-thinking, from the iconic record sleeve to the totemic ending to "A Day in the Life". There are very few moments in pop music history in which you can mark a clear before and after, in which almost everything changed. In the UK, it's arguably happened only five times, and on just four instances in the U.S. (Thriller here; acid house and punk there, and Elvis everywhere, of course); in both nations, the Beatles launched two of those moments.
Excerpt from the latter:
If Sgt. Pepper's Lonely Hearts Club Band doesn't have a concept, it does have a theme. It's a record about England in the midst of whirling change, a humorous, sympathetic chronicle of an old culture convulsed by the shock of the new—by new music and new mores, by rising hemlines and lengthening hair and crumbling caste systems. In short, it's a record about the transformations that the Beatles themselves, more than anyone else, were galvanizing. Playing Sgt. Pepper's for the umpteenth time, you marvel at what generous-spirited revolutionaries the Beatles were. Compare the "Don't trust anyone over 30" rhetoric of the Beatles' 1960s fellow travelers to "When I'm 64," the sweetest song about old age ever created by a rock group. Then there's "She's Leaving Home," which hitches one of McCartney's prettiest melodies to a lyric that sympathizes on both sides of the generation gap—with the runaway girl who is "meeting a man from the motor trade," and with her grief-stricken parents: "We gave her most of our lives/ Sacrificed most of our lives/ We gave her everything money could buy." It's a remarkable feat of the artistic imagination, but it may as well have been reportage: Many British parents were saying such things back in the spring before the Summer of Love. Forty years later, if you listen closely, you can hear what Sgt. Pepper's Lonely Hearts Club Band sounded like that morning at Mama Cass' flat in England in 1967. It sounds like England, in 1967.