In 1966, the Beatles weren’t new to the concept of drugs. Their shows in Hamburg in the early 1960s were fueled by the appetite stimulant Preludin, which gave them what seemed like unlimited energy to play for hours, until it wore off. And then they’d simply pop more. If Rubber Soul was known as the pot album, then Revolver would be known as the LSD album.

It would be foolish to attribute the innovative surge the group experienced during the Revolver sessions to LSD alone, but it certainly didn’t hurt when it came to opening up their minds to musical possibilities that might not have been seen otherwise.

Although Rubber Soul had hinted at new directions in the Beatles’ music, it was the group’s June 1966 release of the single “Paperback Writer” that drove it home. Its b-side track “Rain” tinkered with backwards vocals, experimental bass effects and new technologies at Abbey Road Studios.

To achieve all that they did in 1966, they couldn’t have done it without a little help from their friends—in this case, some friendly competition from other artists in the music scene at the time. Bob Dylan’s landmark album Blonde on Blonde was released, which included, arguably, two of his greatest songs — “Visions of Johanna” and “Just Like a Woman.” The Rolling Stones’ also released Aftermath, which consisted — for the first time in the band’s history — songs all written by Mick Jagger and Keith Richards. It also included a variety of instruments not usually associated with rock albums, including marimbas, the Japanese koto and the dulcimer.

Lennon and Dylan hanging out in the back of a taxi…high.

Despite how the press reported it back then, the Beatles were friends and hung out with all of these artists. They listened to each other’s music, compared notes, and got high together.

They also benefitted from friends in the studio. Most notably, producer George Martin, who by all accounts, was the closest thing there was to a “fifth Beatle.” Martin helped guide the group’s innovative sound— from the double-string quartet on “Eleanor Rigby” to the French horn obligato on “For No One.”

But it was also thanks to 20-year-old engineer Geoff Emerick, who was promoted to replace veteran Norman Smith. Emerick is most notable for his work on the first track recording for Revolver, Lennon’s “Tomorrow Never Knows.” By recording his voice through a Leslie speaker, it gave it the faraway sound the song is known for, which was something that had never been done before. It was ideas like this, along with the microphone placement for McCartney’s bass and Starr’s drums, that paved the way for the way studio recordings were done after Revolver.

But it wasn’t just the studio effects and instruments that made Revolver stand out from the rest of the Beatles catalog. It was the songwriting.

Revolver starts out with the Harrison-penned piece “Taxman,” a first for the lead guitarist. No other Beatles album previously led with a Harrison track, not to mention such a political song, with “Taxman” about England’s 95 percent taxation on the wealthy. Then there was “Dr. Robert,” about prescription pill dependency. And “She Said, She Said,” a song about death, inspired by an acid trip with Peter Fonda and members of the Byrds. From a songwriting standpoint, Revolver was one of the most emotionally-complex albums that had been released in the 1960s at that point.

Some music historians claim Ringo’s drumming on “She Said, She Said” as some of the best in pop music history.

All four Beatles were arguably at their artistic peak in 1966. But during the Revolver sessions, the group also showed signs of crumbling as each member started pursuing their own creative paths.

In August, the Beatles performed their last live show of their final tour, at San Francisco’s Candlestick Park. And as 1966 neared its end, the group began work on “Strawberry Fields Forever,” a song written by Lennon that would guide the band’s musical direction in the coming year.

In 1967, when Brian Wilson first heard the song, he pulled over in his car, broke down in tears and said, ‘They got there first.”