Right from the first time we went to America in 1968, Led Zeppelin was a word-of-mouth thing. You can't really compare it to how it is today.

You never knew what was going to happen in concert. It was a really exciting prospect to go onstage, and you can hear that in the live recordings ... wherever we were and whatever year it was, we always went onstage determined to do our best.

I've never regretted anything I've ever done.

I have a voracious appetite for all things, worldly and unworldly.

The blues appealed to me, but so did rock. The early rockabilly guitarists like Cliff Gallup and Scotty Moore were just as important to me as the blues guitarists.

But to put out a greatest hits on one CD was totally impossible, I just couldn't do it. The best compromise was to put out two CDs - Early Days - which is what it is - and Latter Days.

I'm obsessed - not just interested, obsessed - with folk music, street music, the parallels between a country's street music and its so-called classical and intellectual music, the way certain scales have travelled right across the globe. All this ethnological and musical interaction fascinates me. Have you heard any trance music? That's the thing.