I hear that Discworld is used as a name of a genre, that the term has that kind of currency. "That may be the case, but I don't know quite what people would mean. It is, if you'd like, just a different kind of fantasy genre. I've seen the word used in British newspapers to refer to some situation that is ridiculous and absolutely true at the same time, like, 'It couldn't possibly happen on Discworld.'"

Tell me about Thief of Time. "Time is a resource pretty much like water, and there isn't quite enough of it to go around. So there is a highly secret organization--I suppose you could say they're sort of like Shaolin monks, very big on living in secret valleys up in the mountains. And they make certain there is enough time to go around by taking it from those areas where it's being wasted, like the rural areas, and pumping it into the cities where there is never enough. You know when you go to the rural areas where it seems so quiet and nothing ever changes? It's because the time is actually being used up in the city. They've been doing this for thousands of years."

At number 26, is Discworld at a point now where you didn't even imagine it would be? "When I wrote the first three, I thought maybe I'd write five; by the time I had written seven, I thought maybe I'd write 10; by the time I got to 15, I realized that this was something I'd be in for the long haul."

You must be very happy. "I'm very rich! And quite happy as well."