Having been interested in permaculture for a year or so, i've heard the Holmgren principles bandied about. This book explains, in fairly simple terms mostly, the rationale behind each of the 12 principles. At times it is heavy on scientific stuff, but it goes to show how deeply it's all been thought through. It's been really helpful in putting my mind at ease about certain things, there's a particular passage where he talks about the use of fossil fuels as being evil. When in fact it's not, but we over-use them. So it helps to know that you're not expected to dig 3 acres by hand, get a machine in and do it. It's a one time thing and it can be justified. And another passage where he compares solar cells to photosynthesis and makes the point that the embodied energy of the things doesn't really match green leaves for efficiency, after billions of years of evolution. So grow trees and burn them for electricity. At least that's what I think he's saying. It's a real head-scratcher of a book and something i'll keep coming back to over the years i'm sure, and a good one to give people to stimulate a bit of conversation on these issues, being as important as they are.