Single-handedly reinventing the image of the classical chamber ensemble over the last four decades, The Kronos Quartet has been on a journey which has taken them from the international to the interplanetary, via a list of collaborators that reads like a who's who of creative forces in music, theatre and politics, from Bartók to Bowie, Meredith Monk to Matmos, Nine Inch Nails to Noam Chomsky.

Besides a recent festival of 40th anniversary concerts in New York, this year Kronos have opened up a characteristically new direction in their work in the shape of their score for the film Dirty Wars, opening in UK cinemas on November 29.

George Crumb - Black Angels

The American experimental composer's intensely dark and strange 1970 work for "electric string quartet" written "in tempore belli" during the Vietnam War.

"I remember reading that [Pierre] Boulez had said that the string quartet was dead. When I heard Black Angels I knew he was wrong. Hearing it in 1973 was the reason I started Kronos. I really didn't have any choice because of the magnetic quality of that experience. We've been playing it ever since. We're still playing it this year.

"At that time, hearing Black Angels brought into focus the very confusing, fractured world that most people of my age were a part of. On one side, there was the experience of the Vietnam War and everything that was doing to society. On the other side, the world of music was at a particular place where you'd have Jimi Hendrix over here and Schubert over here and they didn't seem to have a connection. Then I heard Black Angels and everything felt connected and for a moment the world made sense. I started Kronos because I wanted to celebrate that music. It was also a transformation for me.

"From our very first performance of that piece in the spring of 1974, we've reinterpreted it many, many times, with subtle changes in the staging and the pacing, always searching for the best way to do it. As you know, there have been numerous other American-led wars since then and Black Angels feels to me as new and as vital as it did the first time I heard it."

Alternative Radio (Kronos with Howard Zinn and David Barsamian, Carnegie Hall, 2005)

Live collaboration with broadcaster and writer Barsamian and historian and activist Zinn.

"I first met David Barsamian nearly 20 years ago and quickly came to think of him as an extraordinary person. He has the largest archive of alternative ways of interpreting the news. His radio shows appear throughout the United States, frequently in the middle of the night, but you always get a sense of what's really happening. Through him, I was able to meet Howard Zinn.

"In 2003, I became a grandfather, just as Bush and Cheney were organising the American-led invasion of Iraq. I had this dread of what this child would be a part of, in this world with yet another war, so I wanted to talk to people with real perspective. All of a sudden I felt this powerlessness in the face of these events that so many people got swept up in. Even me, a violinist. I didn't need to be a policy expert, or a counter-revolutionary; it's just common sense. So many innocent people have suffered and died, while weapons builders experiment with their newest inventions. But if you're a musician and you see the world going nuts, what are you going to do about it?

"Becoming a grandparent, I've become increasingly idealistic. I want the world to be a safer place and it was Howard Zinn that gave me renewed energy. As musicians know, music has to happen in a safe place. Concert halls can't be bombed-out shells of their former selves. They have to be places of quiet and places where music can be appreciated."

Nuevo

Kronos' exploration of Mexican music spanning 100 years, released as an album in 2002.

"Nuevo really began in 1995. In April of that year my son died suddenly and in thinking about the Christmas holiday, I realised that it would be a good thing for my family, my daughter, my wife and me to go to a neutral place. I had been in Mexico before and realised that the way life and death are celebrated and intersect with daily life is very different. I thought that would be a good place for us to go. The Nuevo album is a direct result of those ten days we spent there. Every sound on that recording is something we experienced there. In a way, the album is a little thank you note to the culture of Mexico for helping us.

"All those years between the beginning of 1996 and around 2000, when the idea finally took shape, I'd been thinking about it and thinking about it and with a lot of help from Gustavo Santaolalla, Osvaldo Golijov and many other friends we were able to put this together.

"Three albums resulted from that tragedy. The rest of my life is probably going to be spent dealing with it in various ways. Early Music (1997) is the album actually dedicated to my son. Then we made the Caravan [2000] album. I was in Prague the year after he died, on the day of his birthday, and I realised that I could listen to the same note and at one moment it would incredibly sad, the next moment ecstatic. Caravan is the beginning of an exploration of that one quality in "note making". Then, with Nuevo, I wanted something boisterous, colourful, ecstatic, something that reflected the energy of a really happy 16-year-old boy."

Dirty Wars Soundtrack

Based on the book by Jeremy Scahill, and directed by Richard Rowley, Dirty Wars is a 2013 feature-length documentary on recent American intervention in Afghanistan and other overseas territories.

"I was invited to see the film and the producers said they had in mind the music of Kronos. It was a shocking experience to see this film. When you see innocent children being killed, suffering, the misuse of power that exists, you start hearing things inside. How could you not? They asked me if I'd be interested in being the music supervisor. I didn't really know what that was, but I liked the fact that our music was a part of that film.

"What happened for me, on a musical level, is very basic. Watching the film, I heard a chord; the first chord of the first string quartet music I ever listened to, in fact, Beethoven's Opus. 127. It's a chord I've carried with me for 52 years now. We went into a recording studio and made variations on that one chord, transformed from major to minor. If you listen very carefully to the soundtrack, to some of the very soft connecting links between scenes, you can hear the same chord I heard when I saw the film for the first time.

"A lot of people probably think we'd disregard or have no use for music of the past such as Beethoven, but for me there's a period of about, let's see, 78 years, from the day Haydn started writing quartets to the day Schubert died, when the string quartet as an art form got this unbelievable foundation. Created by four white guys living in one city: Haydn, Mozart, Beethoven and Schubert. As far as I'm concerned, I think that Kronos is very, very fortunate, in that we get to participate in an art form with that kind of foundation. But what I've wanted to do ever since I was fourteen is to find out about all those other people in the rest of the world: what do they sound like and how can we bring some other aspects of life into this music?

"I have a lot of warm thoughts about the work of those four composers (Haydn, Mozart, Beethoven, Schubert) and I hope the work Kronos does somehow extends the reach of what can be done with two violins, a viola and a cello. Those composers' music doesn't need to be smashed away, but nor does it need a fence building around it. My feeling is that the greatest note by a human being has not been made yet. There's still a lot to do.

Terry Riley - Sun Rings

90 minute audio/visual work written in ten 'spacescapes', utilising plasma wave recordings made by NASA scientists alongside the sounds of the Kronos Quartet.

"We first met Terry in 1979 at Mills College [Oakland, California], where he was teaching. The very first time I met him I felt very close to him. I thought, "this guy has GOT to write music for us." In 1979 he hadn't written any music on paper since In C (1964). He'd moved away from the idea of notating his music, improvising and studying with Pandit Pran Nath, the great North Indian singer. So it took a while for him to start writing for Kronos, but he's been writing for us ever since. In fact, I just heard yesterday that his new piece in honour of Kronos' 40th anniversary has just been finished and I cannot wait to see it.

"Sun Rings is just so expansive, so community oriented, so thrilling. The piece came about after our manager called us while we were on tour and said, 'NASA want to know if you'd be interested in using some of the sounds recorded on the Voyager expeditions.' And I said, 'I didn't know there were any sounds out there - have them send them to me!' I played the sounds to Terry because I wanted to see his expression. Then I knew immediately he was the right person to spend the time, the effort and the energy to bring these worlds together.

"It was started in August 2001, then after September 11 happened he rethought the entire piece. On September 12 he heard the great American poet Alice Walker chanting on KPFA radio, "One earth, one people, one love," and with her permission that became the lyrics of the final movement of Sun Rings. Through Sun Rings we not only got to know the physicist who invented the machine that recorded all of the sounds on the Voyager expedition, but we also got to work with Willie Williams, the stage designer who designed U2's live shows for many years. The production didn't have a director, but it had its own gravitational sense. Everyone knew what they needed to do. It was an amazing moment in our work. I think Terry Riley is one of the great forces in life."

A Chinese Home (Kronos With Wu Man)

Ongoing theatrical project with the pipa (ancient lute-type instrument) virtuoso Wu Man, based on traditional Chinese music and new commissions for string quartet and pipa.

"About 22 years ago, Chen Yi and her husband Zhou Long [both composers] invited me to dinner at their home just after a performance of Henryk Górecki's 3rd Symphony. They played me some video recordings of different kinds of music and instrumentalists from China. At one point this young woman was on the video playing this instrument - the pipa. You know, most people who play the violin can remember the first time they heard Jascha Heifetz. For a pianist it's maybe like hearing Glenn Gould for the first time or something. Well, when I heard Wu Man that night I realised the brilliance of her instrumental performance, the command of her instrument, the vividness in the way she played. I'd never heard anything like that before.

"As happens with me, there was this kind of magnet - I had no choice. Somehow we had to play with her. It turned out Wu Man had recently moved from China to the United States, to New Haven, Connecticut I think it was. She spoke very little English and I don't speak any Chinese, but eventually we got to know each other.

"Over the years we've tried to create a repertoire together. Terry Riley wrote The Cusp Of Magic for us, Tan Dun wrote Ghost Opera and, more recently, Philip Glass wrote a piece for us. For the performances of the resulting evening, A Chinese Home, we brought in a director for the first time in Kronos' history, Chen Shi-Zheng [more recently director of Damon Albarn's Monkey: Journey To The West]. It's an hour-long theatre piece, attempting to take an audience through some of China's history in the 20th and 21st Century.

"What I've learned about Wu Man is that she's very modest. It's just not possible to know the extent of her knowledge. Out of all the people I know she's probably the most knowledgable. She's the one I go to for advice about Chinese music and culture."

Steve Reich - Different Trains

Reich's landmark 1988 piece for string quartet and the pre-recorded voices of Holocaust survivors.

"When I first met Steve he had no intention of ever writing string quartet music. He came to San Francisco and we had a meeting. Then he sent me Vermont Counterpoint, the [multitrack and live soloist] flute piece, and he said, 'Here you go, if you want to make a string quartet out of it, go ahead!' What he didn't realise is that the western concert flute is my least favourite instrument in the universe. It has to do with a unfortunate high school relationship! Shortly after that we were playing a concert and I thought, 'We should open with Clapping Music by Steve Reich.' And after that I wrote to Steve and told him we'd just played his 'first string quartet'. Anyway, we remained friends and eventually he brought [composer] György Ligeti to a performance of Terry Riley's Salome Dances For Peace, the two hour quartet, and after that Steve accepted the commission from [prolific arts philanthropist] Betty Freeman, who was a friend of American music for many, many years.

"I will always go for whatever's the most personal idea. For any composer, go for that, try to find the 'core' experience. Different Trains totally changed the way Kronos plays concerts. We premiered it in London at the Southbank Centre with a team of engineers. In those days, we played it using reel-to-reel tape. Then we did a performance in The Hague and there the team weren't quite so experienced. Then the third performance, somewhere in the United States, was a disaster and it became very clear that we needed to have our own dedicated sound engineers. So, as a result of Different Trains, every concert we've done since 1988 has been with a sound system and in the middle of 88 we engaged out first sound engineer. It's a very pivotal piece in our work. Different Trains has opened up possibilities for so many new directions."

Nunuvut (Kronos with Tanya Tagaq), You've Stolen My Heart (Kronos with Asha Bhosle), Kronos with Dawn Upshaw, Kronos with Diamanda Galás

Four projects with four unique vocalists - Canadian Inuit throat singer Tagaq, otherwise known for her work with Björk, Bollywood legend Asha Bhosle, classical soprano Upshaw, and the unclassifiable Diamanda Galás

[The Quietus] I was going to accuse you of cheating, by listing four separate projects as one choice. Am I right in thinking you regard your collaborative work with extraordinary singers as one, ongoing whole?

"That's exactly the case. I should have also put Alim and Fargana Qasimov - they should be there. All these amazing singers. As you know, Tanya's in a world all by herself. And, of course, Asha, the most recorded voice in musical history. What we did with Diamanda has never been released - those few people who've heard it have told me it's the best Diamanda has ever sounded. It pains me that it's not available and maybe one day we will be able to release it. Then there's Dawn Upshaw. The work we've done with Dawn… well, what she brought to the Lyric Suite of Alban Berg is just unbelievable.

"The ongoing love of voices is something that's part of Kronos, whether it's Paul McCartney or Tom Waits, you name it, we love voices. I've got my list of voices I'd still love to work with but, believe me, it's pretty extensive."

Pieces Of Africa

Kronos' bestselling 1992 album of music by composers from Africa.

"As with all our adventures, Pieces Of Africa did not start out as an album; it started as one piece, which gradually became something else. When I was in high school, I heard some amazing recordings of various kinds of music from Africa and thought, 'Wow, I hope some day I can be part of something that sounds so warm, so vibrant.' It wasn't until 1984 that a piece by an African composer was written for Kronos: Kevin Volan's White Man Sleeps. Then Terry Riley introduced me to Hamza el Din, who wrote the second piece. Shortly after that Philip Glass introduced us to Foday Musa Suso. Around 1991 I realised we had to make an album.

"What I've found is that wonderful musicians exist in every city in every country of the world and I want Kronos to celebrate that, and celebrate relationships. With each of our composers I'm hoping they're going to write their very best piece, no matter what their background might be, or whatever their instrument might be or whatever their voice might be. In that way, I think our work is consistent: we simply play music with ourselves and other people."

Kronos@40 at the Lincoln Centre Out of Doors festival, 2013

"All our albums, Caravan, Nuevo, Early Music - we could make them again with totally different music. We could make another Pieces Of Africa tomorrow, there's so much music been written since. All of these projects have been ongoing.

"I curated a week-long festival, the idea was to celebrate Kronos at 40. There were five performances. We started with music by Fela Kuti and went through to brand new music by Ukrainian composer and singer Mariana Sadovska; a piece called Chernobyl: The Harvest. I don't know if you've heard of her yet, but she's amazing. Basically it's music that had existed in Chernobyl [before the disaster]. Now people who had lived there are returning. They want to spend their last days in the place they grew up.

"Each day of the festival had a different theme. The fourth day was a family music day which was so much fun. We had the Brooklyn Youth Chorus and a group called Face the Music which is made up of junior high and high school kids who play the music of living composers. This kind of thing did not exist when I was their age. It's fabulous! We're hoping to celebrate where we're at now, and what our musical culture is now, so on the last night we ended up with a piece by Dan Deacon in which the audience use their cellphones to participate in the music. It felt like we were being launched into our fifth decade.

"I want Kronos to always celebrate that aspect of the world we live in and participate in; we've never lived in an age with more promise and musical vitality."