This year sees the tenth anniversary of the original publication of Northern Lights, the first in the trilogy, and it has now sold 1.2 million copies across the world. It has been translated into 39 different languages, has been adapted for the stage at the National Theatre and is in the process of being made into a film.

Much has been written about His Dark Materials by literary critics and scholars, but Philip himself doesn't like to talk about the story too much - he would rather you read it for yourself, use your imagination and draw your own conclusions.

He says: 'As a passionate believer in the democracy of reading, I don't think it's the task of the author of a book to tell the reader what it means. The meaning of a story emerges in the meeting between the words on the page and the thoughts in the reader's mind. So when people ask me what I meant by this story, or what was the message I was trying to convey in that one, I have to explain that I'm not going to explain. Anyway, I'm not in the message business - I'm in the once-upon-a-time - business.'

So, His Dark Materials is a series to be read and enjoyed, not discussed, dissected and deliberated over. More than a million children have already done just this over the past ten years - and many more will do so for decades to come.

You can find out more about Philip Pullman and his work on his own website, www.philip-pullman.com, and a synopsis of His Dark Materials can be found here.
We had a chat with Philip to see how he feels about Northern Lights ten years on.

This Autumn is the 10th anniversary of Northern Lights. Why has it been so popular?
I don't know! If I knew, I'd have published it 30 years ago instead of ten. But I suppose it's partly to do with the fact that it's concerned with the matter of growing up, and that's something all of us are going through, or have gone through, or will go through, so it's something of interest to everyone.

Why do you think this popularity has lasted for so long?
Well, I suppose I must have got something right!