Fifty years ago, the television show united children’s education, puppetry, and songs. Pop stars have been singing the Muppets’ tunes (and vice versa) ever since. How many ways can you sing about the letter B? On “Sesame Street,” that question has many furry answers. Since its inception in 1969, the public television show has redefined what it means to teach children through TV, with music as its resounding voice. Before “Sesame Street,” it wasn’t even clear that you could do that; once the series began, as a radical experiment that joined educational research and social idealism with the lunacy of puppets and the buoyancy of advertising jingles, it proved that kids are very receptive to a grammar lesson wrapped in a song. Big-name stars lined up to make guest appearances that have become the stuff of legend (Stevie Wonder and Grover; Loretta Lynn and the Count; Smokey Robinson and a marauding letter U). And long before inclusion was a curriculum goal, “Sesame Street” made a point to showcase Afro-Caribbean rhythms, operatic powerhouses, Latin beats, Broadway showstoppers and bebop alongside its notably diverse cast. “Sesame Street is one of the earliest examples of a musical I experienced,” said Lin-Manuel Miranda, who grew up adoring “I Love Trash” and called its singer, Oscar the Grouch, “a character so singular that he changes the way you see the world at large.” “I learned from ‘Sesame Street’ that music is not only incredibly fun, but also an extremely effective narrative and teaching tool,” he added in an email. “On top of that, their songs are the closest thing we have to a shared childhood songbook.” Miranda began composing for “Sesame” not long after his first Tony win in 2008; his friend Bill Sherman, a fellow Tony winner, became the “Sesame” music director the following year. Today, with online viewership in the hundreds of millions, the series still hosts pop superstars — Janelle Monáe, Romeo Santos, Ed Sheeran, Sia, Katy Perry, Bruno Mars — on the updated streetscape where Nina Simone sang “To Be Young, Gifted and Black” in 1972. Now, as it marks its 50th anniversary — after 4,526 episodes, not to mention specials, movies, albums and more — the legacy of “Sesame” is clear: It impacted the music world as much as it shaped TV history, inspiring countless fans and generations of artists. And the show is still innovating, finding ever more ways to sing out loud. In the late ’60s, when Joan Ganz Cooney, a television producer, and Lloyd Morrisett, a psychologist and philanthropy executive, set out to develop “Sesame Street,” their aim was to build school preparedness and narrow the educational gap between lower- and upper-income children. They brought in a Harvard professor for pedagogy advice and borrowed from commercial TV to create memorable characters, including Jim Henson’s Muppets. Research also showed that children were more attuned when they watched with caregivers, so in came the celebrity appearances (on the second episode, James Earl Jones enunciates the alphabet in theatrically sloooow tones) and parodies of songs that mom and dad would know. The sonic identity of “Sesame Street” had many creators: Jon Stone, the first head writer and a longtime producer and director, helped conceive the theme song, and the writer Jeff Moss (like Stone, an alum of “Captain Kangaroo”) gave us “Rubber Duckie,” “The People in Your Neighborhood” and “I Love Trash.” But the person most associated with the show’s musical style was its inaugural music director, the classically trained, Harvard-educated composer and jazz pianist Joe Raposo. In the early years, when “Sesame” did a now unheard-of 130 hourlong episodes a year (it sometimes aired as often as five times a day) Raposo’s output was prodigious: He wrote over 3,000 pieces for the show, original compositions that could range from a few seconds to full-blown production numbers. “He would receive the cans of film from the office, watch them overnight and score them,” said his son Nick Raposo. With a pencil and a legal pad, he wrote “everywhere,” his son said, including in taxis, sometimes handing his freshly jotted arrangements off to the music coordinator through the window. The first few seasons were definitely trippy; you could blame the era, or the pace. In those early years, “he was in the studio or on set probably 18 hours a day,” Nick Raposo said. “They would just sleep under the mixing board and wake up and start mixing the next day.” (Like many of his early “Sesame” compatriots, including Jim Henson, Joe Raposo died young, in 1989, at 51.) Music on “Sesame” functioned in three ways: as backing tracks for animation and film clips (a lonely orangutan looking for a zoo playmate, say); as live performances by well-known guest artists; and as songs for the human actors and Muppets to sing. Raposo, who loved Jelly Roll Morton and Chopin, fado and klezmer, wrote “C is for Cookie” — Henson originally developed Cookie Monster for snack commercials — and “Bein’ Green,” which took on extra poignancy when it was performed by Lena Horne and later Ray Charles, who told puppeteers that he identified with the song’s message about getting comfortable in your own skin, whatever the shade. Among the “Sesame” breakthroughs was the belief that — in a show that had characters of different ethnicities living in harmonious urban proximity — the music should be multicultural, too. “Joe really pushed for that,” said Christopher Cerf, a Harvard classmate who joined him at “Sesame” in 1970 and went on to write hundreds of songs over the next 45 years. And as the “Sesame” universe expanded, it pulled more and more major musical talent into its orbit. The jazz musician Toots Thielemans, who performed with Benny Goodman, Ella Fitzgerald and Charlie Parker, played harmonica on the theme song. Grace Slick provided vocals for animated counting sequences. The guitarist in the first “Sesame” traveling band was Carlos Alomar, who toured with James Brown and then wrote the riff for David Bowie’s “Fame.” Alomar’s replacement, who was 19 or so and showed up at his audition with a Muppet-esque green-tinged Afro, was Nile Rodgers. It was his first real paying gig as an artist. “Sesame Street” was “part of my musical development,” said Rodgers, the Chic frontman and Grammy-winning producer. The harmonies were highly sophisticated. “You got to be a real player to play that stuff,” he said. “When we played ‘People in Your Neighborhood,’ it was almost like we were a fusion band.” Famous Faces in the Neighborhood The show’s first year set the tone for its mission of social and emotional uplift, with folky guests like Pete Seeger and Odetta. But as “Sesame Street” exploded with attention, the pop firmament rolled in. In 1973, Stevie Wonder arrived as an episode-long musical guest, to teach Grover about vocal dynamics. With his full band on set, he performed “Superstition” live to an audience of children — not professional actors — head-banging and playing maracas in their ’70s acrylics. It quickly became one of TV’s iconic musical moments. By then, “You really could approach almost anyone and have a shot at getting them to come on,” said Cerf, the longtime songwriter. “And people started to call us, especially celebrities who had just had kids.” In his first appearance, in 1973, Johnny Cash brought his young son to the taping — and in the ’90s returned with his granddaughter and daughter Rosanne Cash. Throughout the late ’70s and ’80s, the artists that graced the Sesame stoop were a crossover with the Billboard charts: Carly Simon, Linda Ronstadt (doing a mariachi number!), Diana Ross, Paul Simon (upstaged by a little girl), Billy Joel. In the ’90s and 2000s, there was Celine Dion, the Dixie Chicks and Destiny’s Child. For generations of children watching at home or at school, the message was that even world-famous stars could be accessible. “No one was too big for ‘Sesame Street,’ which made it so cool,” said Patrick Stump, the Fall Out Boy frontman, who credited the show with invigorating his curiosity about music and more. Norah Jones vividly recalled Cab Calloway’s 1981 performance, in white tie and tails, of a Muppet call-and-response “Hi-De-Ho” as “definitely the first time I saw any jazz musicians.” The show remained committed to spotlighting artists who might not be familiar to mainstream audiences. The jazz percussionist Max Roach appeared in 2000; the Latin queen Celia Cruz in 1987. And there was always room for classical stars, often repeat visitors. The violinist Itzhak Perlman made several appearances in the ’80s, and still gets recognized from them. Because the show mixed music so seamlessly with other segments, “it became a classical pill that was very easy to swallow,” he said. (Perlman, who has used crutches since he had childhood polio, also took part in an influential 1981 segment that addressed his physical difference.) Lang Lang, the star pianist from China, began watching the show at 15, when he first came to the U.S. — precisely because he saw people like Perlman on it. He was invited to appear early in his career, and considered it a crossover coup. “Sesame,” he said, connected classical music to kids’ everyday lives, in a way that stripped it of its highbrow connotation. In his appearance, he went a step further: “I was trying to speak like Elmo, to be funnier.” (The producers, he recalled, told him to just be himself.) Being on “Sesame” is simultaneously surreal and deeply comforting. If you grew up with it, it’s as familiar as your childhood bedroom — but a fever-dream version, with a cast of adults scooting around the floor on cushioned dollies, staring at monitors while they speak in incongruously high-pitched or gravelly voices that travel out of their perpetually aloft arms. And yet, guest artists almost instantly forget that there’s anyone inside Ernie or Abby Cadabby. “I knew, of course, it was a puppeteer,” said Jones, of her 2004 bit, spoofing her Grammy-winning “Don’t Know Why” with a song called “Don’t Know Y.” And yet, “I definitely felt like it was Elmo and the letter Y. I could feel, like, his heart beating; it was really like — whoa, he’s real.” Bursting into tears is also common. Tracy Chapman needed a break to compose herself during her 1998 performance; Gloria Estefan, who connected with Sonia, Luis and Maria, the show’s trailblazing Latino characters, “cried when she walked in, because she said she was able to see herself and identify with somebody on TV,” said Carmen Osbahr, who performed alongside her as the Spanish-speaking Muppet Rosita. When R.E.M. came on to do “Happy Furry Monsters,” a takeoff on their hit “Shiny Happy People,” they hung around the set all day, adding jokes to their number and watching other segments being produced, said Cerf. “That happened all the time,” the songwriter said. “I was there when Melissa Etheridge came, and she wanted to sit in Big Bird’s nest before she left.” Harry Styles, the One Direction star, also “had to meet Big Bird,” said Bill Sherman, the show’s music director. “And Will.i.am needed to talk to Grover.” Like Lin-Manuel Miranda, Chance the Rapper is an Oscar guy. “I always just felt like he was misunderstood,” he said. When he came on to do a theatrical scene with Cookie and Elmo, he also invented a bit for himself and Oscar. “People are so happy to be on the show that they’ll almost do anything,” Sherman noted, with some glee. “You’re like, ‘stand on your head and count to 10!’ They’re like, ‘sure!’” In 2009, Carrie Underwood appeared, in voice only, as the character Carrie Underworm, an orange crawler with long blonde hair. The lessons “Sesame” taught “have impacted me in ways that I don’t even realize,” she wrote in an email. “My favorite ‘friends’ on TV were always singing and having fun, and I felt like I was a part of it. That’s a lot of what I try to do as an artist today.” Chance, too, said “Sesame” affects him even now. The Raposo classic “Sing,” he said, “felt like it was a song telling me not only to just be confident and keep going in all ways, but specifically as an artist to this day, it makes me feel like I should be creating.” How does a “Sesame” song come to be? It’s started the same way for the last half-century: with a curriculum. Each year, outside experts outline pressing academic and social issues; from that, and the input of Dr. Rosemarie Truglio, the show’s senior vice president for curriculum and content, an educational theme for the season is built. Episodes can have individual goals, too, and preschool basics like numbers, letters and reading-readiness are perennials. Then, the scriptwriters step in (“Sesame” writers generally only pen lyrics). “Little kids have short attention spans,” said Christine Ferraro, a “Sesame” writer. “If it’s too talky, you’re going to lose them.” Ferraro, who started at “Sesame” right out of college as a secretary and has now been a writer and lyricist there for 26 years, is responsible for one of Elmo’s most popular numbers, “Brushy Brush,” a celeb-filled ode to brushing your teeth. It has nearly half a billion YouTube views, and the gratitude of legions of toddler parents. Cerf is known for his rock parodies: He was behind the Grammy-nominated “Born to Add,” a Bruce Springsteen take-off featuring Bruce Springbean and Cookie as Clarence Clemons on the album cover. (Though “Sesame” normally has its choice of stars, there are some that have remained out of reach. Despite entreaties, the Boss has never appeared. Neither has Madonna, Paul McCartney or the Rolling Stones.) After a song has lyrics, Sherman and his team score it. Brevity and repetition are key; “Sesame” songs are mostly just verse and chorus, but they’re tuned for catchiness. “You try to make the verse a hook, and then the chorus even more earwormy, if possible,” Sherman said. Demos go to producers and artists for approval and production suggestions, but they must also pass the ultimate litmus test: his two daughters, now 6 and 8. “They’re very honest, and if they aren’t humming it or singing it, I will usually throw it away and write it again,” he said. His track record is stellar: “What I Am,” the first song he co-wrote, for Will.i.am, became a viral hit, with more than 88 million views, and won an Emmy. A number for Janelle Monáe, “The Power of Yet” — inspired by her hit “Tightrope,” and written “in my basement in like 20 minutes” — was so convincing that she told him it could appear on her next album. From musicians, said Sherman, that’s “the best compliment I ever get.” If Sherman doesn’t compose a song himself, he sends it out to his team of seven or eight musicians, a who’s-who of Broadway, movie and pop heavyweights, including Chris Jackson, a star of “Hamilton,” who contributed to something like 100 songs over the last decade; Benj Pasek and Justin Paul, who composed for “La La Land” and “The Greatest Showman;” Jennifer Nettles of the country band Sugarland; and Stump of Fall Out Boy, who will have a recurring, synthy theme song in the 50th season. “Stylistically, it’s so far afield from any stuff I do,” Stump said. Even for veterans, the curriculum goals — Season 50: “The Power of Possibilities: Embracing Oops and Aha’s”— don’t always make for easy assignments. On the other hand, said Cerf, “You know that if you can’t figure out an ending, you can just have Cookie Monster eat whatever you’re writing about.” Lookin’ at you: a drawer-full of supplies at the Jim Henson Company studio in Queens, N.Y.CreditVincent Tullo for The New York Times Composing for a furry creature is its own head trip. “Nothing is more surreal than getting an email with an attached .pdf with the ‘vocal ranges’ of the ‘Sesame Street’ Muppets,” Lin-Manuel Miranda shared. “It’s like receiving a national security briefing.” The show has endured long enough that children who were reared on its voices are now creating them. When Matt Vogel auditioned to play Big Bird (he took over as the originator, Caroll Spinney, retired), he prepped by listening to a classic Big Bird album — but he also based the vocals on his own memories of the character and the show in the early ’80s. “I still hear the sound effects and the instruments in my head,” he said. The music and puppeteering also inform each other. Except for Cookie, the Muppets only have four fingers (three fingers and a thumb — because, essentially, it’s cuter, said Jason Weber, creative supervisor at the Jim Henson Company, where all the Muppets are made). When they play instruments, it involves dexterity — Rosita strumming her guitar takes four hands, three of them fur-clad — and imagination. “Abby plays the guitar lefty, and she can only move her hand in a certain direction, so you have to keep it in this, like, punk vibe,” Sherman said. Whereas Hoots the Owl, a saxophonist, can really wail. One person does his hands and another, his mouth, “so you can nail all these really cool saxophone licks.” The multi-instrumental Elmo — he plays the violin, piano, drums and more — occasionally has his arms elongated to fit his repertoire. There are Muppet instruments, too, which present their own conundrums: Does a pair of Muppet bongos, for example, have one face or two? And what is the personality of a bongo drum, anyway? These are the workaday conversations that Henson people have with their Sesame colleagues. “It’s a weird job,” Sherman said, laughing. What unites the cast and crew is their fervent dedication to the “Sesame” mission. Carmen Osbahr, who grew up in Mexico, recalled learning English from its songs. Mesmerized since childhood, she worked on “Plaza Sésamo,” the Mexican version of the show, and was recruited by Henson and crew to help create Rosita. “The same happiness, sadness — all the feelings that music brings — and everything that ‘Sesame Street’ has to give, I really wanted to be part of it, so I can pass it along,” she said. Sherman knows the weight of the legacy acutely, and uses it as his spark. “It feels like a relay race, and I’ve been handed a baton,” he said. “I’ve written hundreds of songs about the letter A, and I’m always trying to get better,” he added. “How can I make a song so that every kid, when they sing this song, all they can think about is the letter A?”