Twyla Tharp loves Billy Joel. And their Broadway baby is called Movin' Out.

"I've been listening to Billy's music as long as he's been writing it," Tharp says. "And I've always thought it was extremely danceable." So one day, just about two years ago, the renowned director and choreographer began thinking about creating a dance narrative based on the famed singer-songwriter's words and music — "because he's such a good storyteller." The idea Tharp had was to use Joel's music in conjunction with her own vision of a crucial period in American history, beginning with the years of the Vietnam War, "a period we both lived through."

Movin' Out, at the Richard Rodgers Theatre, spans those two difficult decades, from 1967 to 1987. It tells the tale, in song and dance, of six lifelong friends — Brenda and Eddie from Joel's song "Scenes from an Italian Restaurant," Tony and Sergeant O'Leary from his "Movin' Out," Judy from "Why, Judy, Why" and James from "James." The cast of 27 includes John Selya, Elizabeth Parkinson, Keith Roberts, Ashley Tuttle, Scott Wise and Ben Bowman. Michael Cavanaugh, a Billy Joel sound-alike, sings 24 classics and surprises written by Joel, a native of Long Island who in the last quarter century has been an icon of American popular music.

Movin' Out is "a story told without language," Tharp says. "Yes, there are Billy's lyrics, but it's told through a different medium. We don't want audiences to come in expecting a standard Broadway musical. There's a narrative, but there are no book scenes. The movement and the action tell the story — the experience, the emotional resonance, comes from action rather than language."

In Tharp's nearly 40-year career, her accomplishments include founding her own dance company, creating more than 125 dances, choreographing three Milos Forman movies — "Hair," "Ragtime" and "Amadeus" — and directing and choreographing the 1985 Broadway version of Singin' in the Rain. On television, she co-directed "Baryshnikov by Tharp," which won two Emmy Awards. And in 1992, she won a John D. and Catherine T. MacArthur Foundation Fellowship — also known as the genius grant. After she thought of using Joel's music, Tharp says, she tried it out with several of her dancers and made a tape, to see "if it was a doable idea, if the music really did dance. And then I called Billy," she says. "I told him that we had never met, and that he didn't know me, but I asked him to come see it. He came and looked at the tape. He said he liked what he saw, and he said, 'O.K., go for it.'"

Joel, who in his long and phenomenally successful career has won five Grammys, has told interviewers that he wasn't sure what Tharp wanted to show him — that he was concerned it would be a "cringe-fest" — but that he loved it, that old songs "sounded new again."

Tharp says that she finds the narrative, the story of Movin' Out, "difficult to talk about. In part that's because it's told without language. But it comes down to three main points. At the beginning, there's the post-World War II idealism that suffused this country, the sense that if something was broken we could fix it. This is our simple, fablelike way of beginning. There's a car — yes, it's a 1960's Mustang — and the car has broken down. And Eddie gets out of the car and starts to fix it. In those days, that was the American spirit."

But then the Vietnam War intervenes — and with it, says Tharp, comes "the corrosive effect that the war had on our national ethos, that it created in our culture a rift unlike any other in our country's history — that we couldn't make the world over in our image in that time, any more than we can today."

It is with that feeling, she says, that the curtain comes down on Act One. "Act Two is easy. It's about survival. And we come out of it, as I feel Billy's music does, with the belief that the cup is half full, not half empty." The goal of Movin' Out, Tharp says, is to make audiences feel that they, as well as the characters, "have really made a progression.

"We want them to feel that the dancers are amazing, and the band is great, and the songs are wonderful. But we also want them to see that the people have made a voyage, that in front of the audience's eyes they have grown up — and that it's not easy to do. It's a redemptive ending, and it has a sense for the audience of being rejuvenating. There's an old-fashioned word for it. It's catharsis. That's what I think we all strive for in the theatre."