Until the 1990s, Steve Reich seemed the least likely of the leading contemporary composers to write an opera. For a quarter of a century his whole development was rooted in instrumental works, with voices and texts, when they were used, generally treated instrumentally, and sectional musical structures that seemed unlikely to lend themselves to the dynamic of music theatre.

Then in 1993 he unveiled The Cave, a large-scale collaboration with his wife, the video artist Beryl Korot. It explored the roots of Christianity, Judaism and Islam through the story of Abraham, and the iconic significance to those religions of the Cave of the Patriarchs on the Palestinian West Bank. Reich and Korot called their work a "documentary video opera", but it was never intended as opera as we know it. Interviews with members of all the faiths involved were shown on an array of screens, together with location footage, while an ensemble of instrumentalists and singers provided a musical counterpoint and commentary, with the speech patterns of the interviewees providing the starting point for much of the score.

Now Reich and Korot have produced Three Tales, which was presented complete for the first time this week at the Vienna Festival. It is a much tighter, more incisive work than The Cave, at the same time more visually and musically complex yet more straightforward to perform. The advances in computer techniques over the past decade have allowed Korot to manipulate complex patchworks of images in a single frame. The visual effects are thrillingly virtuosic but can now be projected on a single screen, while an ensemble of instrumentalist and singers functions as a chorus, commenting on and reinforcing what is seen and heard on the video.

Rather than the biblical past of The Cave, Three Tales deals with the technological present, focusing on three key moments in 20th-century history: the crash of the Hindenburg airship in 1937; the atomic-bomb tests on Bikini atoll in 1946; and the cloning of Dolly the sheep in 1997. Korot's source in the first two tales is newsreel footage from the time. For Dolly, which leads on from genetic engineering to an exploration of artificial intelligence and what the 21st century could produce, she and Reich make use of specially filmed footage of interviews with leading authorities in the field, from Richard Dawkins and Stephen J Gould (disagreeing, typically) to Steven Pinker and Marvin Minsky. The whole 65-minute piece is a huge achievement, visually and musically, which gets more and more engrossing as it goes on. With each tale longer than its predecessor, the trajectory seems perfectly judged.

Three Tales really defies classification. Reich and Korot describe it as music theatre, but it is a very personal take on the genre, and very much the amalgamation of their talents. Reich's music surveys many of the techniques he has pioneered throughout his career, and the use of repeated phrases in the final section takes him right back to where he started in the 1960s, experimenting with tape loops and phasing. It is hard to see, though, what other composers could borrow from their methods.

Berg was the first composer to include film in any opera (in the second-act interlude in Lulu) and since then numerous composers have flirted with the combination of music and projected images - most of them, it must be said, with very limited success. Certainly no one has made such a symbiotic amalgam between the two media as Reich and Korot, or made it seem so naturally effective. The pair have not begun to think about their next joint project - each has a pile of solo commissions to fulfil - but it is hard to imagine how they could top Three Tales. By the time they start another collaboration, though, the technology will have again leapt forward, and yet another range of possibilities will have opened up.

· Three Tales will be repeated at the Royal Theatre Carr¿, Amsterdam (00 31 2053 0110), from June 13-15 and the Barbican, London EC2 (020-7638 8891), from September 18-21.