Back in 2022, Joker director Todd Phillips announced plans for a sequel with an Instagram post that revealed the title — Joker: Folie à Deux — but little else. When Lady Gaga joined the cast as Harleen Quinzel, better known as Harley Quinn, the picture became clearer. It clarified again with the rumors that it would be a musical, though Phillips and others involved with the film played coy about this up to the premiere. Where the original Joker looked to Martin Scorsese’s Taxi Driver and The King of Comedy for inspiration, the sequel takes the shape of a jukebox musical drawing on a variety of 20th-century songs, including pop hits, old standards, and tunes from Broadway shows and movie musicals.

As might be expected, given Joker’s grim, grimy version of realism, the musical numbers in Folie à Deux are often ironic, a way to soundtrack the delusions of protagonist Arthur Fleck (Joaquin Phoenix). Sometimes, they underline the action, as characters belt out boisterous songs while chaos erupts around them. Occasionally, though, Phillips plays it straight, letting a sad song serve a sad scene and a happy one express joy, however short-lived it might be.

Neither approach works consistently, to the point where it’s often unclear what the filmmakers want to accomplish via their musical homages. There isn’t a bad song in the movie, however, and the eclectic choices help keep it unpredictable. And part of that unpredictability is the wide range of sources Phillips draws from, none of which are obvious directions for a dark drama. Here’s where Joker: Folie à Deux’s most notable tunes came from and pointers to some of the renditions that inspired the sequel.

Joker: Folie à Deux opens with a sequence animated by Sylvain Chomet, the French writer and artist behind The Triplets of Belleville and The Illusionist. This spin on a classic Warner Bros. cartoon finds the Joker doing battle with his own shadow. Jackie (Brendan Gleeson), a guard at Arkham State Hospital, takes an intense interest in Arthur, the would-be clown doing time for multiple murders. But Jackie also likes to sing, and at one point, Joker’s identity crisis gets a callback when Jackie reprises this song. It’s a lonely lament in which the singer is left with only other aspects of himself for company, and it doubles as commentary on Arthur’s deflated state as the film begins.

This often-covered song became one of the biggest hits of 1940 twice: The influential vocal harmony group The Ink Spots took it all the way to No. 3 on the pop charts, as did Tommy Dorsey and His Orchestra, also hitting the No. 3 spot that same year with some help from a scrappy young vocalist named Frank Sinatra.

No other song in Joker: Folie à Deux appears as often as this uptempo spiritual number, which becomes a kind of theme song and rallying cry for Arkham’s residents. Though inextricably tied to New Orleans, the song has no credited composer, and its repetitive lyric has numerous iterations and can be stretched to whatever length performers want. (Sometimes in a performance of this song, you’ll hear about the moon turning red with blood. Sometimes it’s the horsemen of the apocalypse. Sometimes both.) It’s one of those songs that belongs to no one and everyone.

But Louis Armstrong’s 1938 version did more to popularize it than any other recording. Like most renditions, Armstrong’s “When the Saints Go Marching In” sounds so joyous, it’s easy to overlook that he’s singing about the end of the world, though those apocalyptic undertones probably help explain how it’s used in Phillips’ film.

Arthur first meets Lee Quinzel (Lady Gaga), soon to be the object of his amour fou, when he passes a music therapy session as Lee and other inmates are singing “Will the Circle Be Unbroken?”, a hymn that emerged from the same era as “When the Saints Go Marching In.” While it’s an inspirational song, just like “Saints,” “Will the Circle Be Unbroken?” is focused on how lasting happiness can’t be found in this life, only in the life beyond.

Composed in 1907 by Charles H. Gabriel and Ada R. Habershon, it’s been covered countless times, though the most famous version, recorded by the Carter Family in 1935, keeps the tune but changes the words and alters the title to “Can the Circle Be Unbroken (By and By).”

A holdover from Joker’s final scene, this song of sanguine defiance makes a couple of appearances in the sequel. First recorded by Marion Montgomery in 1963, it became a hit after Frank Sinatra included it in a 1966 television special, A Man and His Music — Part II. Folie à Deux features several songs associated with Sinatra, but even without them, the film would bear the Chairman of the Board’s influence. When singing, Phoenix’s body language often recalls Sinatra’s, and Phillips draws inspiration from images of Sinatra in concert, never more directly than when framing Joker alone on a stage, illuminated by a single spotlight. It’s an instance of one entertainer with a dark side paying homage to another.

“When the Saints Go Marching In” and “Will the Circle Be Unbroken?” both emerged directly from different strands of religious music. Composed in 1930 by Harold Arlen, with lyrics by Ted Koehler, this number has roots in the secular world, but looks to church for inspiration.

The song took on a new life when Judy Garland sang it in the 1950 musical Summer Stock, in which she plays a farmer bitten by the desire to perform when a troupe of actors takes up residence on her property. Garland later made it a cornerstone of her concerts, and it became nearly as closely associated with the singer as “Over the Rainbow.” Continuing a Folie à Deux theme, it’s a plucky, upbeat song about death and all the ways the world in which we live can’t compare to the afterlife.

Speaking of Arlen and Koehler, they’re also responsible for this number, sung by both Gleeson and Lady Gaga at different points in the film. It’s another song deeply associated with Sinatra, who had a hit with it in his comeback year of 1953. But others sang it before him, including Cab Calloway and Sinatra idol Bing Crosby.

Sometimes, a song just needs the right artist to make it immortal. Ron Miller and Orlando Murden wrote “For Once in My Life” for Motown in 1965, and several of the label’s other artists took a crack at it with limited success. So did Nancy Wilson and Tony Bennett, the latter making the charts by giving the song a tender ballad treatment in 1967.

Musically, Bennett’s rendition doesn’t have much in common with Stevie Wonder’s better-known 1968 smash, but both singers invest the song with openness and vulnerability to match a lyric that captures the feeling of someone surprised that they aren’t alone anymore. In one of Folie à Deux’s rawest moments, Arthur uses it to express the same sentiment.

Folie à Deux makes numerous visual references to classic musicals — in one early moment, a group of Arkham guards hold up dark umbrellas, which suddenly sport colors straight out of The Umbrellas of Cherbourg — but only one musical makes a direct cameo. Arthur and Lee sit together at an Arkham movie night where they watch the classic 1953 Vincente Minnelli musical The Band Wagon. Its famous numbers include this paean to show business, which includes a couple of details that could have been written specifically for Arthur, including the opening one about a “clown with his pants falling down.” (The film’s run-up to the song even includes a reference to Bill Robinson dancing on stairs, which surely strikes a chord with Arthur, no stranger to stair-dancing.)

“That’s Entertainment” also includes the line “The world is a stage / the stage is a world of entertainment,” which brings to mind the yearning for fame that drove Arthur in Joker. In the sequel, Lee joins him for a song about wanting to be seen and appreciated by the people they used to know — and, it’s implied, the people who used to look down on them. It’s sung by Shirley MacLaine in the 1969 film Sweet Charity, Bob Fosse’s directorial debut. But Fosse’s wife, creative partner, and muse Gwen Verdon originated it on stage, in a musical inspired by Federico Fellini’s Nights of Cabiria.

The Bee Gees were just starting out when they recorded this song, a highlight of the group’s 1967 album Bee Gees 1st. Doing their best imitation of American soul music, the Gibb brothers scored a hit with a lament sung from the perspective of someone who feels like they’ll never be on the receiving end of love.

An expression of abject loneliness, it doesn’t seem like a song that would easily lend itself to a duet. But Lee and Arthur’s rendition isn’t exactly traditional, either. Joker and Harley are far from the only artists to attempt the song. Some performers have taken it on quite successfully, like Nina Simone and the Flying Burrito Brothers. The Bee Gees’ version remains the best known, though Simone’s tops it for drama and intensity.

After Burt Bacharach and Hal David penned this song in 1963, it made the rounds of recording artists in search of their next hit. Richard Chamberlain, Dionne Warwick, and Dusty Springfield all recorded it, but it never caught on like many of Bacharach and David’s other ’60s hits. That changed in 1970 when the Carpenters scored a hit built around Karen Carpenter’s plaintive vocals, which gave the love song an undercurrent of melancholy without changing a word.

Some of Folie à Deux’s song selections seem less than obvious — but not this one. “The Joker” originated in Leslie Bricusse and Anthony Newley’s allegorical 1964 musical The Roar of the Greasepaint — The Smell of the Crowd, and it opens with the line “The Joker is me.” A little on the nose? Sure. But if you’re making a Joker jukebox musical it would be hard to pass this one up. And it’s sung by a crying-on-the-inside clown not unlike Arthur Fleck, which must have made it impossible to ignore.

The Roar of the Greasepaint — The Smell of the Crowd is now better known as the source for some well-liked songs than as a play, spawning “Feeling Good” and “Who Can I Turn To?” in addition to “The Joker,” which attracted covers by Sammy Davis Jr. and Shirley Bassey, among others. Newley originated the role himself, and performs the song on the cast album.

Another selection from a Bricusse/Newley musical, “Gonna Build a Mountain” plays an even more prominent role in the film. A highlight from Stop the World — I Want to Get Off, first staged in 1961, the song also seems like an obvious choice for the film to draw from, thanks to a protagonist who plays the lead role, Littlechap, in clown makeup.

That detail isn’t evident in the song, but it’s of a piece with Folie à Deux’s soundtrack in other ways: It’s another gospel-inspired number, this one built around the dream of building “a heaven from a little hell.” Newley originated this role as well, though Tony Tanner assumed it in the 1966 film adaptation. But the highest-profile version of the song belongs to Sammy Davis Jr., who played Littlechap in a ’70s stage revival, and in a TV movie version retitled Sammy Stops the World.

Belgian-born singer-songwriter Jacques Brel enjoyed great success in the Francophone world, then picked up an even wider audience when poet/singer/songwriter Rod McKuen began translating his lyrics into English, sometimes loosely. “If You Go Away (Ne Me Quitte Pas)” reached the English-language world first, and it remains one of Brel’s most-covered songs. It’s also one of his saddest, even with McKuen’s slightly more hopeful lyric.

American singer/comedian Damita Jo recorded the earliest English version, followed by, among others, Glen Campbell, Marc Almond, Ray Charles, Neil Diamond, Cyndi Lauper, Brenda Lee, Frank Sinatra, Dusty Springfield, Scott Walker, and McKuen himself. It also became a favorite of Shirley Bassey, whose slow, smoky version sounds like someone having their heart destroyed piece by piece.

Stay through the credits of Joker: Folie à Deux, and you’ll hear Phoenix singing the film’s most obscure track, albeit one beloved by its creator’s passionate cult following. A fixture of Austin, Texas, for most of his adult life, artist and musician Daniel Johnston began his recording career via homemade, self-distributed cassettes filled with his eccentric, inimitable lo-fi music, and he became a favorite of the indie rock world. Kurt Cobain could be frequently seen wearing a Johnston T-shirt.

Though Johnston struggled with mental health issues throughout his life, he remained a prolific recording artist until his death at age 58 in 2019. The sweet, wistful “True Love Will Find You in the End” became one of his best-known songs, thanks in part to Beck’s cover version, but Johnston’s own performance captures the aching sincerity evident throughout his work.