It is possible to trace the start of one of the most enduring and productive relationships in the music industry back to one night, 50 years ago, at a gig in New York's Greenwich Village. In the audience were Alan and Marilyn Bergman, two people who had ahead of them not only stunning careers as lyric writers but one of the most successful marriages in showbusiness.

Marilyn and Alan had already been married for two years by then, and so it is not their relationship that is the issue here, but the one between them and the unknown singer they saw perform that night - Barbra Streisand.

In the decades since then, Streisand has sung over 50 songs written by the Bergmans - among them You Don't Send Me Flowers, The Way We Were and the entire score for the first film Streisand directed, Yentl. And now this month, Streisand pays tribute to her favourite lyricists by releasing What Matters Most, an album devoted entirely to the Bergmans' work.

"This is not just long professional relationship" says Marilyn, speaking on the phone from their hom in Berverley Hills, "but a deep and lasting personal one."

The album contains many songs that Streisand has not sung before. Some were composed specifically for others in mind, including Nice 'n' Easy, which was written for Frank Sinatra.

To write the lyrics for yentl, they had to go cheder for a year

"They wanted an easy-going song for Sinatra's album that matched his personality. We could have only written it for Sinatra," says Alan.

"He made a one-act play out of that song," adds Marilyn.

The way Sinatra sings it, Nice 'n' Easy sounds like foreplay. The way Streisand sings it, it has an altogether more tender message about nurturing a relationship - not just consummating it. Which is not inappropriate considering that in the notes for her new album Streisand writes that the Bergman's lyrics work so well because the couple - who are both in their 80s and have been married for 52 years - are still in love.

"Their spectacular marriage gives the lyrics an authenticity, making them both deeply personal and, at the same time, completely universal," says Streisand.

"You can only write from what you are and what you know. In many instances, if we were writing about a relationship, we would have to look at our experience," says Marilyn.

Certainly that turned out to be the case with one of the Bergmans' most popular and evocative songs – the lyrical and surreal stream of consciousness that is Windmills of Your Mind. In the movie, The Thomas Crown Affair, the song soars while on screen Steve McQueen catches thermals in his glider. The creative process began straightforwardly enough. Director Norman Jewison showed the entire movie to the Bergmans and then spooled back to the glider scene.

"I'd like you to underline the anxiety of McQueen's character," said the director. Composer Michel Legrand, who would later work with the Bergmans on Yentl, flew in from Paris and stayed with the lyricists so that they could work every waking hour.

"Michel wrote eight melodies," remembers Alan.

"Each one was very different from the others," adds Marilyn. "Each said something totally different about what was happening on the screen."

But the couple remembered something that director Jewison had said as he and his songwriters watched McQueen's Thomas Crown fly through the air - "it could all come crashing down". And so Marilyn and Alan knew that the song had to not only paint a portrait of a smart and troubled guy, but describe something totally different from what was on the screen.

"If we had written a song that said 'what a lovely day to fly a glider', what would have been the point?" says Alan.

After sleeping on it, the three decided on a melody as dizzying as the loop-the-loops performed by Crown in his glider. But the images conjured by the Bergman's lyrics came from an entirely different place.

"Like a circle in a spiral/Like a wheel within a wheel/Never ending or beginning/On an ever spinning reel."

"When I was seven I had my tonsils out," explains Marilyn. "And as they gave me the ether anaesthetic I remember this circular descent into a sleep state. Alan had had a similar experience. And that's how we got the idea to write for Michel's circular melody."

So it turns out that Windmills is more stream of unconsciousness than consciousness.

The process for coming up with the lyrics to Yentl could not have been more different. Alan and Marilyn are both Jewish - Brooklyn born and raised, both born in the same hospital in fact. But although Alan had been barmitzvhed and Marilyn had always "loved being Jewish", neither were equipped to write about the attitudes and traditions of an Orthodox community. So they went to cheder.

"We studied for about a year," says Alan. "We talked to rabbis. One was Orthodox and the other was Reform. I think she was the first or second woman to be ordained." The result was yet another Academy Award to add to the those won for Windmills of Your Mind and The Way We Were. There have been 16 Oscar nominations in all.

Songwriting collaborations usually take the form of one composer and one lyric writer - not one composer and two lyricists.

"It's unusual I know," says Marilyn. "Someone said it's like three people making a baby."

A few days before this interview took place, the Bergamans received a telephone call from one of their old friends and long–time collaborators, Tony Bennett. "He called to tell us that Amy Winehouse had died. He was so sad," says Marilyn of the 85-year-old Bennett who had recently recorded with Winehouse.

"He said she was extremely talented," says Marilyn.

"It was terrible, terrible news," echoes Alan.

Working with enduring performers such as Streisand and Bennett - and Sinatra, Johnny Mathis, Ray Charles and Michael Finestein too, among many others -perhaps the Bergmans have an insight of just how much has been lost with the death of Winehouse.

Not that the lyricists have finished adding their own contribution to music. Just as they have for the past 52 years, they continue the work that has resulted in some of the greatest popular songs of all time. Perhaps surprisingly for a husband and wife team, it is a process that involves no argument, and certainly no creative tantrums. "Maybe occasional disagreement," says Alan, whose description of one of the most productive songwriting collaborations in the world could not be more understated.

"We just go into a room," he says.

Barbra Streisand's new album 'What Matters Most' is out August 22 on Sony Music.Visit www. barbrastreisand.com