Bjork: Tree’s Company.

Greatest Hits and Family Tree are in stores now.

Bjork. What do you say about Bjork Gudmunsdottir that hasn't been said before? Superlatives and hyperbole are useless - they have all been used up. She and the word 'unique' are one and the same. Bjork is the most profound and significant female composer and songwriter in the world. That's true. But, really, when you get down to it, Bjork is just, well, Bjork.

Bjork's realm is the edge of avant yet melodic, modern classically structured electronic pop music (often with strings) that bears no discernible similarity to the work of any other artist. And when she sings, it is as if the world has stopped and wants to listen. Over four studio albums - Debut, Post, Homogenic and Vespertine, a remix album Telegram and Selmasongs, the soundtrack to Lars Von Trier's chilling, Dancer In The Dark (in which she also delivered an Academy Award nominated performance) Bjork has successfully explored a personal world that makes no concession to popular taste or fad.

Yet, at 37, the woman who grew up in a communal - but not hippie - household in Reykjavik listening to Pink Floyd, Jimi Hendrix and Cream, and studying classical flute and piano, remains restless - despite just having her second child, a sister for 18-year-old son Sindri, doesn't wish to settle and is certain that her life's work is largely unfinished.

"If I put something out in this world, it would be the courage to go and invent things," she said recently. "I would die for my art - there have been times when I've been touring for 15 months and I'm literally crawling on stage, and people say what's more important, your health or tonight, and I always say tonight. But I'm not here to act, I'm here to make music. Life is short, and I haven't even done half the things I want to do."

"I never stood up and said: I don't want to be like the others. I didn't simply have the need to disassociate myself. I was always busy with my immediate environment, with sounds or with lava rocks. I must have seemed strange to many people."

Good as the Greatest Hits is in getting across the significant and salient fact that Bjork's music doesn't age - songs such as All Is Full Of Love, Hyperballad, Yoga, Army Of Me, Venus As A Boy and Play Dead, sound as remarkable, unearthly and magical as they did when you first heard them and shook your head in wonder - there is something more important: a straight line, a musical theme, broad but focussed, that is discernible from Human Behaviour, the first track on her first album, Debut (1993), to her most recent track, the Greatest Hits closing, It's In Our Hands.

That is even more apparent in Bjork's, simultaneously released, special box set Family Tree - now this is the real stuff. Five 3" CDs divided into Roots, Beats and Strings collections and one regular size 5" CD of her favourite songs, her own greatest hits, which together represent "the story of how I got to where I am today and in my musical words to say how I developed as a musician."

"After I finished Vespertine, I felt as if I had completed something," she says. "I felt I almost caught up with myself and had got something off my chest I really wanted to do since I was a child and now I feel like I have got a clean slate - a new beginning to start all over again. I sort of feel like I am at a crossroads, so it felt like the right time to put out a selection or more of a retrospect of the story so far. I was ready to put out a collection of the singles, but I also wanted to put out a story of how I got there, and not a bunch of words that have been documented so much already in tons of interviews. More important was the emotional and worldly things, in a musical way - in my musical words and to say in this way how I have developed as a musician.”

In the end though it's all about emotion. Her music and that extraordinary voice evoke the most extreme of emotions. To many of her fans she is both an inspiration and a great romantic. With Bjork’s music there is always a huge emotion washing over the listener.

"I guess that is the nature of my work - by being the sort of person that preached about emotions and emotional rules," she says. "Being emotional doesn't mean that you are stupid, like you could still go haywire and arrange and orchestrate things, things that are usually considered quite academic or clever. Just as long as you use emotion as the structure, as long as there is a heart to it, it is okay. So because of that, most of my songs are very precious to me. And if that means you only get a record every three years - they are the 10 peaks in those three years.