Over the past 50 years, Jane Greenwood has designed the costumes for around 130 Broadway shows. She has worked with just about every actor imaginable - from Katharine Hepburn to Scarlett Johansson. But her focus, when I interviewed her the other day, on the eve of her collecting an honorary Tony this Sunday, was to extol not her own gifts but those of her collaborators. Her assessment of Tony Shalhoub, her fellow nominee this year for Act One(Greenwood is not only receiving an honorary statuette but is in contention for a competitive one), is typical. Of his ability to perform the quick costume changes required for his three characters, she says, "It's a lot of work, but he makes it look effortless." 

The same could be said of Greenwood. It was she and her colleagues, after all, who made those lightning-fast transformations possible. She explained the process of fitting clothes to character to actor. 

"Everybody talked to me about the book Act One but I had never read it. I grew up in England, in Liverpool, where it was less known. When I did read it, I found it so charming, and James Lapine's play of it was delightful, but I thought: how do I do the clothes for so many actors, all of whom play so many characters?" 

She and her associate, Daniel Urlie, started by calling costume shops and asking what they had from the 1920s and early 1930s, the play's timeframe. They went to London, to the fabled costume houses Angels and Cosprop. They consulted shops in Los Angeles and Boston. "We amassed racks and racks of clothes," Greenwood said, "but still there were gaps, so we ended up having some of the costumes made." 

All the outfits worn by Andrea Martin, for example, were made. "It took a couple of fittings to really nail her Aunt Kate. We gave her a little padding, for roundness, and it was important to find the right hat. Hats are crucial because they complete the silhouette." 

Of paramount importance was making all the costumes easy to get in and out of - a true challenge for an era of elegance, 1920s and 1930s, a time that was, Greenwood contends, "the peak moment for men's tailoring." A smooth transformation was especially daunting for Will LeBow's memorable scene as the producer Jed Harris. Why? Because he must dress rapidly in front of Santino Fontana's sheepish young Moss Hart. 

"I'm not going to disclose exactly what we did to help Will," Greenwood said. "Let's just say that there were a few little tricks involved to make it easier for him." 

Such discretion, and such dedication to aiding actors, are crucial for a costume designer's success. "Years ago," Greenwood told me, "an actor said to me: 'Coming to a fitting is a little bit like going to confession. You have to reveal your secrets.'" Which is why, I've always contended, that costume designers are the best-informed professionals in show business. They know where the bodies are buried - and not just those they've fitted. 

Asked about actors who might have been annoying, Greenwood is diplomatic. I pressed her about Katharine Hepburn, with whom she worked on The West Side Waltz and A Matter of Gravity, and the designer said merely: "She had definite ideas." (You don't get to be Katharine Hepburn if your notions are inchoate.) But Ingrid Bergman (O'Neill's More Stately Mansions, in 1967) was "exceedingly gracious" and Richard Burton (a 1964 Hamlet, directed by John Gielgud) was "charming." 

Greenwood has seen the greats mostly in dramas rather than in musicals. "Since I started with The Ballad of the Sad Café and Hamlet, I suppose I got somewhat pigeonholed as someone who designed only plays," she said. "But I have always enjoyed things that are large-scale and romantic, as well." She noted that as a girl in England she thrilled to the ballet, taking in performances by Robert Helpmann and Margot Fonteyn. ("I have not designed much dance but I have done opera.") And the musicals on her bio are memorable: Sondheim and Lapine's Passion, for example. Not to mention Million Dollar Quartet, the Broadway extravaganza with Elvis and Johnny and Jerry Lee and Carl. "I loved those sequin jackets at the end of the show," Greenwood remembered. 

Greenwood's upbeat attitude about her career - "I've been extraordinarily fortunate," she said - extends to her record at the Tony awards: before Act One, she was nominated 17 times without winning. "I did get tired of hearing 'you deserved it' each year," she revealed. "Those words aren't part of my vocabulary. I have been so glad to design each show for which I was nominated. A Tony would have been just one more reason for gratitude." 

Moss Hart may not have written a sequel to Act One, but Greenwood said she is working on her own second act. It includes this month's outdoor production in Central Park, Much Ado About Nothing, and a Broadway revival, opening in September, of You Can't Take It With You

That comedy, of course, was written by the stars of the Act One story: Moss Hart and George S. Kaufman. But when I ask Greenwood if she could recycle some of the Act One costumes for it, she replied, "Oh, no. Act One ends in 1930. You Can't Take It With You premiered in 1936. By then, everything has moved on - including fashion." 

Brendan Lemon is the American theater critic for the Financial Times and the editor of lemonwade.com