In the spring of 1969, Paul McCartney telephoned George Martin to ask if he would be willing to work with the Beatles on a new album they planned to record in the months ahead. Martin, who was widely regarded as the most accomplished pop-record producer in the world, had overseen the making of all nine albums and nineteen singles that the Beatles had released in Britain since their début on E.M.I.’s Parlophone label, in 1962. His reputation was synonymous with that of the group, and the fact that McCartney felt a need to ask him about his availability dramatized how much the Beatles’ professional circumstances had changed since the release of the two-record set known as the White Album, in the fall of 1968. In Martin’s view, the five months of tension and drama it took to make that album, followed by the fiasco of “Get Back,” an ill-fated film, concert, and recording project that ended inconclusively in January, 1969, had turned his recent work with the Beatles into a “miserable experience.”

“After [‘Get Back’] I thought it was the end of the road for all of us,” he said later. “I didn’t really want to work with them anymore because they were becoming unpleasant people, to themselves as well as to other people. So I was quite surprised when Paul rang me up and asked me to produce another record for them. He said, ‘Will you really produce it?’ And I said, ‘If I’m really allowed to produce it. If I have to go back and accept a lot of instructions that I don’t like, then I won’t do it.’ ” After receiving McCartney’s assurance that he would indeed have a free hand, Martin booked a solid block of time at Abbey Road studios from the first of July to the end of August.

Thus the stage was set for the Beatles’ tenth studio album, named after the labyrinthine recording complex in North London’s St. John’s Wood that had served as the site of their greatest musical triumphs. Though the tracks from the “Get Back” project, retitled “Let It Be,” would be released later, in the spring of 1970, “Abbey Road” was the Beatles’ last word—the final recordings by the most popular and influential artists of the nineteen-sixties. Now, on the occasion of its fiftieth anniversary, “Abbey Road” has been expertly remixed by Giles Martin, George Martin’s son and protégé, and reissued in a super-deluxe edition that comes with an archive of studio outtakes and a hundred-page book of essays and liner notes that chronicle how the recordings were made. “The Beatles are good even though everybody already knows that they’re good,” the classical composer Ned Rorem observed in 1968, alluding to how the band’s immense popularity confounded the usual notions of discriminating taste. If anyone needs to be reminded of this, this new edition of “Abbey Road” should do the trick.

The unpleasantness that George Martin ascribed to the Beatles stood in stark contrast to the first impression he formed of this oddly named group from Liverpool when they auditioned for a recording test at Abbey Road, in the spring of 1962. At that time, Martin had his doubts about their musical potential, but he was totally charmed by their personalities and repartee. The change he perceived in their behavior toward one another during the course of 1968 was very recent and very real, and it was due to many sources, including the travails of Apple Corps, the Beatles’ farcically naïve attempt to run their own business following the death of their visionary manager, Brian Epstein, in 1967, and their disillusionment with the Maharishi Mahesh Yogi, the jet-setting Indian swami who had filled the void left by Epstein’s death by serving as the band’s brazenly entrepreneurial spiritual adviser. But the root cause of disaffection in the group involved something much more fundamental than its efforts to dabble in hip capitalism or pop mysticism.

By the late nineteen-sixties, the artistic basis of the Beatles’ preëminence in the world of popular music was plain for all to see. Here was a band comprising two of the greatest pop singers and songwriters of their generation, supervised by a supremely innovative pop record producer, and supported by a pair of highly competent and resourceful instrumentalists, one of whom, George Harrison, was emerging as a gifted songwriter in his own right. The axis of the group’s genius, of course, was the collaboration between John Lennon and Paul McCartney. For more than ten years, the musical friendship between these two partners had remained the predominant relationship in both of their lives. But that had changed abruptly in the spring of 1968, when Lennon returned to London from the Maharishi’s ashram in Rishikesh, blew up his marriage, and threw himself into a romantic and creative partnership with Yoko Ono, the fame-obsessed Japanese performance artist who had been pursuing him for more than a year. Ono would later be demonized by the press and the public as the cause of the Beatles’ downfall, but she was more like the solvent that Lennon used to dissolve the bonds of solidarity and common purpose that had distinguished popular music’s most exalted band of brothers. From the moment Lennon and Ono moved in together, in June of 1968, Ono displaced McCartney as Lennon’s collaborator, muse, and sounding board. That she knew virtually nothing about singing, songwriting, or music-making bothered Lennon not at all. If anything, Ono’s brand of dilettantism came as a great tonic to a renowned musical artist whose insecurities about the pretensions of art-making had recently led him to insist to the Beatles’ authorized biographer, Hunter Davies, that “Beethoven is a con, just like we are now.”

McCartney responded to the advent of Ono with all the powers of musical persuasion at his command. The many months of rehearsal and recording it took to make the White Album had brought about a striking improvement in the Beatles’ ensemble playing. The “Get Back” project, as conceived by McCartney, began as an attempt to restore the group’s sense of personal and musical camaraderie by returning it to its roots as a performing band. Toward this end, several of the songs McCartney unveiled at those sessions had been expressly designed to encourage Lennon to share the lead singing with him. (“Two of Us” was self-explanatory, whereas “I’ve Got a Feeling” reversed the pattern of “A Day in the Life” by joining McCartney’s verses to Lennon’s release.) In April, when Lennon sought to celebrate his recent marriage to Ono by rush-recording “The Ballad of John and Yoko” at a time when George Harrison and Ringo Starr were otherwise engaged, McCartney threw himself into the session, making up for absence of the others by playing bass, drums, piano, percussion, and singing harmony on the track. When Harrison and Starr rejoined them a few days later, it marked the start of a productive series of sessions in which all four of the Beatles introduced new songs.

But any hopes that this renewed spirit of collaboration might carry over into the work on the band’s next album were dimmed when a mounting series of business crises caused Lennon and McCartney to square off over whether the group’s financial management should be entrusted to McCartney’s new in-laws, the entertainment lawyers Lee and John Eastman, or to Lennon and Ono’s proxy, the music-business fixer Allen Klein. Klein and the Eastmans, in their efforts to outdo one another, squandered the opportunity for the Beatles to gain control of both their management and music-publishing companies, forcing E.M.I. to pay their record royalties into escrow until the courts could sort things out. For the first time in a long time, the world’s most successful rock group convened to make an album because it needed the money to pay its bills.